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.

server-rs/crates/api-server/src/http_error.rs

@@ -109,6 +109,7 @@ fn resolve_http_error(status_code: StatusCode) -> (&'static str, &'static str) {
         StatusCode::UNAUTHORIZED => ("UNAUTHORIZED", "未授权访问"),
         StatusCode::FORBIDDEN => ("FORBIDDEN", "禁止访问"),
         StatusCode::NOT_FOUND => ("NOT_FOUND", "资源不存在"),
+        StatusCode::GONE => ("GONE", "资源已失效"),
         StatusCode::NOT_IMPLEMENTED => ("NOT_IMPLEMENTED", "功能暂未实现"),
         StatusCode::CONFLICT => ("CONFLICT", "请求冲突"),
         StatusCode::TOO_MANY_REQUESTS => ("TOO_MANY_REQUESTS", "请求过于频繁"),