Match3D & Puzzle: runtime UI, assets, drag fix

Backend: stop treating background music as a required draft asset and remove auto-submit/plan for background music; load persisted generated UI/assets into Match3D agent session responses (added helpers to resolve profile id and fetch existing generated assets). Frontend: make Match3D result preview reuse runtime UI styles, unify runtime settings entry, update PuzzleRuntime to apply immediate pointermove transforms (disable drag transition), use SVG clipPath for merged piece rounding, ensure PuzzleRuntimeShell supplies platform theme classes, and adjust related tests. Docs & logs: update decision log, pitfalls and product docs to reflect these changes.

server-rs/crates/api-server/src/match3d/mappers.rs

@@ -427,26 +427,6 @@ pub(super) fn match3d_bad_gateway(message: impl Into<String>) -> AppError {
     }))
 }
 
-pub(super) fn match3d_background_music_missing_error(message: impl Into<String>) -> AppError {
-    AppError::from_status(StatusCode::BAD_GATEWAY).with_details(json!({
-        "provider": MATCH3D_AGENT_PROVIDER,
-        "message": message.into(),
-        "missingAssets": ["背景音乐"],
-    }))
-}
-
-pub(super) fn require_match3d_background_music_title(
-    plan: &Match3DGeneratedBackgroundMusicPlan,
-) -> Result<String, AppError> {
-    let title = normalize_match3d_audio_title(plan.title.as_str());
-    if title.is_empty() {
-        return Err(match3d_background_music_missing_error(
-            "抓大鹅草稿背景音乐名称为空，无法完成背景音乐生成",
-        ));
-    }
-    Ok(title)
-}
-
 pub(super) fn map_match3d_work_profile_response(
     item: Match3DWorkProfileRecord,
 ) -> Match3DWorkProfileResponse {