feat(kotlin-compose): design system + 33 components + gallery_kt + e2e android emulator + scaffolder fixes

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

types/core/color.md

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+---
+name: Color
+lang: cpp
+domain: core
+version: "0.1.0"
+algebraic: product
+definition: "struct Color { float r, g, b, a; }"
+description: "Color RGBA en floats normalizados [0,1]. Helpers para presets (white/black/transparent), construccion desde u8 (rgba(r,g,b,a)) o desde packed hex (hex(0xRRGGBBAA))."
+tags: [gamedev, color, primitive]
+uses_types: []
+file_path: "cpp/functions/core/math2d.h"
+examples: |
+  Color tint = Color::white();
+  Color red  = Color::rgba(255, 0, 0);
+  Color cyan = Color::hex(0x00FFFFFF);
+notes: |
+  - RGBA en floats por defecto — aceptado por sokol_gfx.
+  - alpha default 1.0 para builders.
+  - Sin gamma correction implicito; el shader decide.
+---
+
+# Color
+
+Color RGBA float usado por sprite_batch (tint), pass clear, debug draw.

types/core/rect.md

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+---
+name: Rect
+lang: cpp
+domain: core
+version: "0.1.0"
+algebraic: product
+definition: "struct Rect { float x, y, w, h; }"
+description: "Rectangulo axis-aligned de floats (x, y, w, h). Usado por sprite_batch, tilemap, hit-tests y AABB queries del stack gamedev (issue 0072b)."
+tags: [gamedev, math, 2d, primitive, aabb]
+uses_types:
+  - Vec2_cpp_core
+file_path: "cpp/functions/core/math2d.h"
+examples: |
+  Rect r{10.0f, 20.0f, 100.0f, 50.0f};
+  Vec2 c = r.center();
+  bool inside = r.contains({50.0f, 30.0f});
+  bool hit = r.overlaps(other);
+notes: |
+  - Helpers: `right()`, `bottom()`, `center()`, `min()`, `max()`.
+  - `overlaps()` es AABB intersection (no-touch = no-overlap).
+  - `contains()` usa half-open `[x, x+w)` como ImGui / texture coords.
+---
+
+# Rect
+
+Rectangulo axis-aligned usado para sprites, hit-tests, AABB queries y tilemaps.

types/core/vec2.md

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+---
+name: Vec2
+lang: cpp
+domain: core
+version: "0.1.0"
+algebraic: product
+definition: "struct Vec2 { float x, y; }"
+description: "Vector 2D inmutable de floats con operadores aritmeticos, length/normalize/dot/cross. Tipo base del stack gamedev (issue 0072b)."
+tags: [gamedev, math, 2d, primitive]
+uses_types: []
+file_path: "cpp/functions/core/math2d.h"
+examples: |
+  Vec2 a{1.0f, 2.0f};
+  Vec2 b{3.0f, 4.0f};
+  Vec2 sum = a + b;
+  float d = Vec2::dot(a, b);
+  Vec2 n = a.normalized();
+notes: |
+  - Definido en namespace `fn::math2d` junto a Rect y Color.
+  - Trivial-copy, constexpr donde aplica.
+  - Sin SIMD intencionado — para hot paths usar buffers planos float[2].
+---
+
+# Vec2
+
+Vector 2D usado por el stack gamedev: posiciones, velocidades, tamaños UV. Operadores `+ - * /` por componente, `dot`, `cross` (escalar 2D), `length`, `normalized`.
+
+Vive en `cpp/functions/core/math2d.h` junto a `Rect` y `Color` para reducir overhead de includes.