fix: bake UI font atlas at physical DPI size so text isn't skinny on standard-DPI

The font atlas was rasterized once at a fixed 16px and point-filtered, then
scaled to a logical size at draw time. On HiDPI it got upscaled (acceptable);
on standard-DPI it got downscaled, and point filtering dropped rows/columns of
the anti-aliased glyphs, thinning stems into a faint "hyper-skinny" look.

Bake the atlas at the real physical size text is drawn at
(16 * GetUIScale() * GetWindowScaleDPI().y), quantized to 4px steps, and rebuild
it via EnsureUIFont() once per frame when that density changes (resize, or
moving between monitors of different DPI). Use mipmaps + trilinear filtering so
downsampling stays smooth. Call sites are unchanged: DrawTextEx still scales the
atlas glyph to the same logical size, only the backing resolution differs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/render.h

@@ -9,6 +9,15 @@ float GetUIScale(void);
 void  DrawTextScaled(const char* text, float x, float y, float baseSize, Color color);
 float MeasureTextScaled(const char* text, float baseSize);
 
+// --- DPI-aware UI font ---
+// InitUIFont remembers the TTF path and bakes the first atlas; EnsureUIFont
+// rebuilds it (cheap no-op when unchanged) whenever the effective pixel density
+// (window UI scale * monitor DPI scale) shifts, keeping text crisp on any
+// display instead of thinning out on standard-DPI screens. Call EnsureUIFont
+// once per frame before drawing text.
+void InitUIFont(const char* path);
+void EnsureUIFont(void);
+
 // --- Colormaps ---
 void GenerateColormapTexture(void);
 const char* ColormapName(ColormapType type);