M13.24: web app depth (WEB-1) — GPU effects in frame workers, OPFS disk cache, storage manager

- GPU in the browser: each frame worker opens its own WebGPU device (Gpu::request_deferred) and
  renders the GPU compositor and GPU effects with deferred readbacks (effectcraft-gpu deferred):
  readbacks keyed by content start with map_async and miss, the pass returns placeholders, the
  layer cache's gate drops inserts, and FrameServer::resume renders again once the device
  delivered. Backend Auto times whole frames per comp in the workers. Frames with effects go to
  GPU workers instead of the page. CPU fallback without WebGPU in workers (?nogpuworkers).
- Fix: a WGSL constant (3.40282347e38) that Chrome rejects invalidated every GPU kernel in Chrome
  (the page's compositor too); a test checks every float literal fits f32.
- Disk cache in the Origin Private File System: workers write sealed frame entries with sync
  access handles (temp file + move), the page keeps the DiskIndex (LRU under the settings' limit,
  at most half the quota) and reads hits instead of rendering; survives reloads; blue cache bar.
- Storage manager: Settings ▸ Disk ▸ Browser Storage (usage/quota, persistent storage, Clear
  buttons, automation ids) and storage.info / storage.persist / storage.clear (StorageHost).
- Docs: web.md (GPU workers, deferred passes, disk cache, storage manager, threading design:
  one engine instance per worker), architecture, preferences, parity (WEB-1), roadmap.
- Tests: deferred passes vs CPU on a real device, placeholder gating, frame server passes and
  Auto, GPU worker routing + disk cache across a reload, storage commands and widgets, store
  usage by kind; smoke test: GPU effect frames in workers with pixel parity, disk hits after a
  reload, storage manager.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

ROADMAP.md

@@ -20,7 +20,7 @@ once.
 | M11 | Animation tools: audio playback, meters and waveforms, Lottie import and export, presets, Motion Sketch, Wiggler, Smoother | Done |
 | M12 | Performance: layer cache, parallel and GPU compositing, disk cache, motion tracking (done); GPU versions of the remaining CPU-only effects | Mostly done |
 | M13 | Puppet tools, paint, Roto Brush, motion tracking, a plug-in API, Timeline depth | Done (Roto Brush and face tracking use classical models; learned models are still to come) |
-| M15 | The web app (WebAssembly, WebGPU) | Done: browser storage, Web Audio, renders and analyses in Web Workers, offline install ([docs/web.md](docs/web.md)) |
+| M15 | The web app (WebAssembly, WebGPU) | Done: browser storage, Web Audio, renders and analyses in Web Workers, viewer frames and GPU effects in frame workers with their own WebGPU devices, the disk cache in the Origin Private File System, a storage manager, offline install ([docs/web.md](docs/web.md)) |
 | M14 | Built for agents: MCP server, command-line tool, control channel; Settings, keyboard shortcut editor, auto-save and crash recovery ([docs/preferences.md](docs/preferences.md)) | Done |
 
 ## How far from full parity