修正陶泥儿运行态图片筛选残留的旧 kind 字面量

- direct_runtime/mod.rs：`direct_game_sources_referenced_taonier_assets` 的 manifest 兜底由 `art-spritesheet | art-spritesheet-slice | game-background` 改为 `IconSpritesheet | Icon | Scene`，恢复对项目自定义图集与背景的收录。
- direct_runtime/mod.rs：同处与 `direct_registered_taonier_runtime_image_paths` 的「切片不得绕过严格校验」排除条件改用 `GameCreationAppAssetKind::Icon`，并顺手把 `icon-spec` 比较改为枚举成员。
- 理由：kind 收紧为枚举后 `as_str()` 只会返回 canonical 名，旧字面量恒不命中，兜底筛选与切片排除同时失效。

apps/ai-game-creator-shell/src-tauri/src/agent/direct_runtime/mod.rs

@@ -2822,15 +2822,17 @@ fn direct_game_sources_referenced_taonier_assets(root: &Path) -> Vec<String> {
                 .into_iter()
                 .filter(|asset| {
                     matches!(
-                        asset.kind.as_str(),
-                        "art-spritesheet" | "art-spritesheet-slice" | "game-background"
+                        asset.kind,
+                        GameCreationAppAssetKind::IconSpritesheet
+                            | GameCreationAppAssetKind::Icon
+                            | GameCreationAppAssetKind::Scene
                     ) && asset.media_type == "image/png"
                         && asset.source.kind == GameCreationAppAssetSourceKind::Canvas
                         && asset.local_path.starts_with("assets/")
                         // Canonical slices are admitted above only after the
                         // full slice manifest/receipt/content validation. Do
                         // not let this generic manifest fallback bypass it.
-                        && !(asset.kind == "art-spritesheet-slice"
+                        && !(asset.kind == GameCreationAppAssetKind::Icon
                             && asset
                                 .local_path
                                 .starts_with("assets/art-spritesheet-slices/"))
@@ -2861,7 +2863,7 @@ fn direct_registered_taonier_runtime_image_paths(root: &Path) -> Vec<String> {
         .iter()
         .filter(|asset| {
             asset.media_type.starts_with("image/")
-                && asset.kind != "icon-spec"
+                && asset.kind != GameCreationAppAssetKind::IconSpec
                 && asset.source.kind == GameCreationAppAssetSourceKind::Canvas
                 && asset
                     .source
@@ -2873,7 +2875,7 @@ fn direct_registered_taonier_runtime_image_paths(root: &Path) -> Vec<String> {
                 // manifest/receipt/content validation. This generic fallback
                 // must not re-admit a slice whose bytes no longer match the
                 // registered receipt.
-                && !(asset.kind == "art-spritesheet-slice"
+                && !(asset.kind == GameCreationAppAssetKind::Icon
                     && asset
                         .local_path
                         .starts_with("assets/art-spritesheet-slices/"))