feature: chat (#36)

* fix(config): load config on demand in get/set instead of asserting

* feat(chat): implement in-game chat box with UTF-8 support

- Add ChatMessage struct and ChatBox widget for displaying and sending messages
- Introduce split_utf8() in text_tools for splitting UTF-8 strings by character count
- Add TimeTools utility (get_time_ticks) for message timestamps
- Update TextField with start_typing/stop_typing methods and set_typing()
- Integrate text input handling in WorldScene and WorldUIManager for chat
- Add utf8cpp library for robust UTF-8 validation and processing
- Add ChatBox rendering and input logic (src/ui/chat_box.cpp)
- Register ChatBox source in CMakeLists.txt
- Fix Renderer::render_lable to skip rendering if VAO is null
- Update credits to include utf8cpp library

* fix(ui): correct chat box layout with dynamic height and bottom anchor

* feat(chat): implement client-server chat messaging

Add protobuf definition for ChatMsg, new packet ID CHAT_MSG (4001), and
handle sending/receiving chat messages on both client and server side.
Wire up UI components (ChatBox, TextField) to allow message input and
display, including a message queue in ClientWorld for thread-safe
processing. Also add default initialization for ChatMessage::time.

* feat(chat): distinguish between send and cancel in chat input

* feat(ui): add background to Label widget and refactor debug overlay

* refactor(ui): decouple ChatBox from image dependencies, allow custom TextField backgrounds

TextField's background is now a generic `Widget` pointer, enabling use of any widget (e.g., `Rect`, `Image`) as background. `ChatBox` no longer creates its own `TextField`; it accepts one via `set_text_field`. Removed `set_d_image` and `set_default_image` in favor of `set_background`. Added a shared default image constant in `default_image.hpp`. Updated `host_game_ui.cpp`, `join_game_ui.cpp`, and `world_ui_manager.cpp` to construct backgrounds accordingly.

* refactor(ui): move width, height, and fill properties to base Widget

Consolidate width, height, and fill (fill_parent, fill_width, fill_height) into the base Widget class. Replace per-widget set_fill(bool) with set_fill_parent(bool), set_fill_width(bool), and set_fill_height(bool).

* refactor(ui): generalize Label background, add ChatBox width method

* feat(chat): implement message expiration after 5 seconds

* feat(ui): add word wrap for chat messages with font width measurement

* feat(audio): implement voice chat using Opus codec

Add voice chat support with Opus encoding/decoding, push-to-talk (V key), and new audio recording infrastructure.

* feat(audio): implement voice chat with Opus codec and streaming audio source

Add AudioStreamSource for continuous PCM playback. Refactor voice send/receive to encode with Opus and stream to a dedicated source instead of per-frame sources. Enable voice transmission over network.

* feat(audio): add spatial voice source with underwater effects

Update voice source to support spatial positioning, low-pass filter, and reverb effect for underwater immersion. Adjust source pool size and low-pass filter parameter. Correct receive_voice parameter type.

* feat(settings): add player voice volume and voice input type options

- Add player voice volume slider and voice input type combo in settings UI.
- Add localization strings for player voice and voice input types.
- Add config overloads for const char* default values.
- Implement voice input types (PTT, always, off) in world scene.
- Refactor WorldScene member order and add load_config method.
- Update audio engine to use player voice volume.
- Downgrade some logging to debug.

* fix(event): delegate error UI events to each handler

Move error UI event check from top of handle_event into each individual
event handler (mouse_move, mouse_button, mouse_wheel, key, text_input).
Also flatten window resize dispatch: all sub-handlers are called regardless
of previous handler return values, and the method always returns false.

* feat(chat): add colored system messages for player join/exit

* chore(logging): reduce verbosity for audio loading and input events

* fix(settings): fix typo in config key "vloume"

* feat(ui): add microphone icon when recording voice

* feat(voice): limit voice message range to 48 units

* chore(logging): downgrade text input log level to debug

* feat(credits): add license identifiers and reorganize license files

* feat: add sensitive word filter for chat messages

Implement AC automaton-based filtering using a sensitive lexicon loaded from a JSON asset file. The filter is applied to both player names and chat messages before broadcasting, and can be toggled via the `sensitive_filter` config option.

* feat(server): add config option to disable voice chat

* fix: correct utf8 validation, add missing include, remove debug log

assets/licenses/OFL-1.1.txt

@@ -0,0 +1,90 @@
+The SIL Open Font License version 1.1 is copied below, and is also
+available with a FAQ at http://scripts.sil.org/OFL.
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded, 
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.