Run the desktop's model layer in the browser

The browser host now stores data through yaak-models compiled to wasm — the
same queries, migrations, cascade rules, duplicate naming and first-run
bootstrap the desktop and CLI use — instead of a TypeScript port of them.

- crates/yaak-web: the wasm crate. boot() registers an IndexedDB-backed VFS
  and calls init_standalone; rpc(cmd, payload, label) answers the models_*
  commands via ClientDb and returns the model_writes it caused; blob get/put
  through blob_manager. Built like yaak-templates (pkg/ committed); the
  build script keeps pkg/ and says so when no wasm-capable clang is present,
  so a desktop bootstrap never depends on one.
- models_ops moves from crates/yaak into yaak-models so the wasm crate can
  use it without the send engine.
- The database lives in a SharedWorker (packages/platform/src/web/worker.ts):
  one process holds the data and pushes writes to every tab, as on the
  desktop. Where SharedWorker is missing or its script cannot be fetched, a
  dedicated worker guarded by a Web Lock takes over and a second tab is told
  so. The worker imports the wasm lazily so a tab's connect is answered
  instantly; the tab reconnects if it isn't.
- packages/platform/src/web loses models.ts, schema.ts, db.ts and the
  BroadcastChannel; commands.ts forwards model commands to the worker and
  keeps the fixed answers and refusals.

Verified in Chrome, dev and production builds: bootstrap, CRUD across every
model type, serde defaults, engine-format ids, Rust copy naming, folder
cascade with per-descendant events, single-event workspace delete, reload
persistence, two tabs coherent, Send declined with a toast, 8/8 reloads
rendering in ~100 ms.

packages/platform/package.json

@@ -9,6 +9,8 @@
     "lint": "tsc --noEmit"
   },
   "dependencies": {
+    "@yaakapp-internal/rpc-schema": "^1.0.0",
+    "@yaakapp-internal/web": "^1.0.0",
     "@tauri-apps/api": "^2.11.0",
     "@tauri-apps/plugin-clipboard-manager": "^2.3.2",
     "@tauri-apps/plugin-dialog": "^2.7.1",