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

include/utf8cpp/utf8/cpp11.h

@@ -0,0 +1,70 @@
+// Copyright 2018 Nemanja Trifunovic
+
+/*
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+
+#ifndef UTF8_FOR_CPP_a184c22c_d012_11e8_a8d5_f2801f1b9fd1
+#define UTF8_FOR_CPP_a184c22c_d012_11e8_a8d5_f2801f1b9fd1
+
+#include "checked.h"
+
+namespace utf8
+{
+    inline void append16(utfchar32_t cp, std::u16string& s)
+    {
+        append16(cp, std::back_inserter(s));
+    }
+
+    inline std::string utf16to8(const std::u16string& s)
+    {
+        std::string result;
+        utf16to8(s.begin(), s.end(), std::back_inserter(result));
+        return result;
+    }
+
+    inline std::u16string utf8to16(const std::string& s)
+    {
+        std::u16string result;
+        utf8to16(s.begin(), s.end(), std::back_inserter(result));
+        return result;
+    }
+
+    inline std::string utf32to8(const std::u32string& s)
+    {
+        std::string result;
+        utf32to8(s.begin(), s.end(), std::back_inserter(result));
+        return result;
+    }
+
+    inline std::u32string utf8to32(const std::string& s)
+    {
+        std::u32string result;
+        utf8to32(s.begin(), s.end(), std::back_inserter(result));
+        return result;
+    }
+} // namespace utf8
+
+#endif // header guard
+