Update Match3D/image-generation docs & code

Adds/updates documentation, assets and implementation for Match3D and puzzle image generation workflows. Key changes: decision logs and pitfalls updated to prefer VectorEngine Gemini for Match3D material sheets and to require edits (multipart) for 1:1 container reference images; guidance added for when to use APIMart vs VectorEngine. .env.example clarified APIMart/Responses config. Many new public assets and PPT visuals added. Code changes across frontend and backend: updated shared contracts, server-rs match3d/puzzle/image-generation handlers, VectorEngine/OpenAI image generation clients, and multiple React components/tests to handle UI/background/container image signing, edits workflow, and puzzle UI background resolution. Added src/services/puzzle-runtime/puzzleUiBackgroundSource.ts and related test updates. Includes notes about multipart HTTP/1.1 requirement and test/verification commands in docs.

docs/design/PLATFORM_UI_NON_PIXEL_REFRESH_2026-04-19.md

@@ -61,6 +61,7 @@
 - 平台层正文、按钮、说明、功能标签统一使用非像素字体
 - 左上角 `陶泥儿 / GENARRATIVE` 品牌字标允许单独做成像素化 logo
 - `GENARRATIVE` 与 `陶泥儿` 都优先直接使用游戏内同款 `Fusion Pixel`
+- 品牌中文主标固定显示为 `陶泥` + 半字号 `儿`，`儿` 必须继承主标同一字体和字号后再视觉缩放到 50%，并与 `陶泥` 底部对齐，随移动端和场景覆盖等比例缩放
 - 品牌字标默认保持正常像素字观感，禁止再叠双层粗阴影或手动加粗到影响识别
 - 品牌字标直接使用字体文件内原字形，不额外做运行时描字、轮廓拼字或伪粗体处理
 - 主标题保留明显层级，但不再做像素描边效果