feat(AppShell): show cached cover art for local Play tab recents

[alexwarren]

Summary

• Local "Recently Played" entries (Electron only) now show their actual game cover art instead of a generic icon, resolved via a new engine-backed query (WasmEditorBridge.ResolveLocalCover, mirroring PlayerCore.GameQuery) that handles both embedded-resource covers (.quest package, legacy .asl/.cas) and sibling-file covers (a plain unpacked .aslx).
• The result is cached on the RecentGame record (coverDataUrl, persisted to recent-played.json) — resolved once at play time (fire-and-forget, off the critical path of opening the player window) or lazily as a one-time self-heal for a legacy/never-resolved entry — since resolving a cover means booting the full engine just to read one field, too expensive to redo on every app startup.
• Also capitalizes the "Recently Played" heading to match the site's other section titles.

Bug fixes found while testing this live

• wasm.ts's loadWasm() self-race: multiple local recents resolving their covers concurrently on mount could each see the WASM bridge not yet loaded and call dotnet.create() a second time ("Runtime module already loaded"), permanently breaking the editor for the rest of that session. Fixed by caching the in-flight load promise, not just its eventual result.
• recent-games.ts file corruption: the read-modify-write cycle behind add/setCover/remove/clear had no synchronization across concurrent calls, so two cards self-healing their covers at once could have their fs.writeFile calls genuinely interleave at the OS level and corrupt recent-played.json outright (a short write's bytes followed by a stray tail fragment of a longer concurrent one) — silently wiping the entire Recently Played list on next read (JSON.parse throws, caught, falls back to []). Fixed with a per-kind write queue plus atomic temp-file+rename.

Test plan

• dotnet build --configuration Release (full solution) and dotnet test --configuration Release — all 336 tests pass
• npx svelte-check / npm run lint / tsc -p tsconfig.json (ElectronApp) — all clean
• Standalone Node harness exercising recent-games.ts directly: carry-forward on replay, in-place cover patch without reordering/timestamp bump, explicit overwrite, no-op on a removed entry, and the exact concurrent-write race that previously corrupted the file (now produces valid JSON with both entries intact regardless of timing)
• Live browser probes against the built WasmEditorBridge/loadWasm confirming concurrent ResolveLocalCover calls resolve correctly with no cross-contamination, and that loadWasm() no longer throws when called concurrently
• Manually verified against real local .quest files (a published package with an embedded cover, and one with no cover set) in a running Electron build

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