feature: hud (#37)

* build: replace FetchContent with direct includes for glm

* build(deps): replace SOIL2 with stb for image and vorbis decoding

* build: replace FetchContent with direct includes for toml++

* refactor(texture): bump block texture size to 512 and disable items tab

* feat: add hotbar system with ItemStack and RowLayout

* fix(ui): restrict Ctrl key handling to typing mode

* feat(ui): add widget border support and highlight selected hotbar slot

* fix(ui): update borders on scale change and correct Image width

- Added update_border() calls in set_scale() for Button, ChatBox, Image, Label, and TextField.
- Fixed Image::width() to multiply by width instead of height.
- Added early return in Widget::update_border() if border is not supported.

* feat(ui): add border visual feedback on slider drag

* feat(ui): add ItemSlot widget and refactor hotbar to use it

* feat(world_scene): add inventory UI and pause type enum

* feat(ui): add item slot tooltip and make window size static

* fix(ui label): account for background offset in width/height

* refactor(ui): centralize item info label in inventory and add update

* feat(ui): add hotbar interaction in inventory UI

* fix(inventory-ui): correct row creation logic for first item

The loop starting at index 0 created a new row on the first iteration
(i % 10 == 0). Shift the loop to start at 1 and adjust modulus condition
to create rows correctly every 10 items.

* feat(block): add name_key for localized block names

Add `name_key` field to all block TOML definitions, enabling per-block localization. Update `BlockData` struct and `BlockManager` with `local_name()` method that returns a localized string via the translation system. Add corresponding entries to `en_US.json` and `zh_CN.json`. Modify inventory UI to use the localized name when displaying block info, and fix a bug where emptying a hotbar slot did not clear the item locally.

* fix(ui): change inventory item slot color from white to gray

* fix(ui): add missing include for std::array

include/glm/gtx/functions.inl

@@ -0,0 +1,30 @@
+/// @ref gtx_functions
+
+#include "../exponential.hpp"
+
+namespace glm
+{
+	template<typename T>
+	GLM_FUNC_QUALIFIER T gauss
+	(
+		T x,
+		T ExpectedValue,
+		T StandardDeviation
+	)
+	{
+		return exp(-((x - ExpectedValue) * (x - ExpectedValue)) / (static_cast<T>(2) * StandardDeviation * StandardDeviation)) / (StandardDeviation * sqrt(static_cast<T>(6.28318530717958647692528676655900576)));
+	}
+
+	template<typename T, qualifier Q>
+	GLM_FUNC_QUALIFIER T gauss
+	(
+		vec<2, T, Q> const& Coord,
+		vec<2, T, Q> const& ExpectedValue,
+		vec<2, T, Q> const& StandardDeviation
+	)
+	{
+		vec<2, T, Q> const Squared = ((Coord - ExpectedValue) * (Coord - ExpectedValue)) / (static_cast<T>(2) * StandardDeviation * StandardDeviation);
+		return exp(-(Squared.x + Squared.y));
+	}
+}//namespace glm
+