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.

DEVELOPMENT.md

@@ -44,6 +44,25 @@ After bootstrapping, start the app in development mode:
 npm start
 ```
 
+## Run the App in a Browser
+
+The client can also run as a plain web page, with no Tauri and no local process
+behind it. Set `YAAK_TARGET=web` and start the frontend on its own:
+
+```shell
+YAAK_TARGET=web npm run dev --workspace @yaakapp/yaak-client
+```
+
+That flag picks the browser host in `packages/platform/src/web/`, which answers
+commands from an IndexedDB database the page owns instead of from the Rust
+engine. Data persists across reloads and is shared between tabs on the same
+origin. Sending HTTP is not available yet — the Send button reports that and
+everything else about the request is still saved. `packages/platform/src/web/README.md`
+lists which commands the browser host implements and which it declines.
+
+Desktop builds are unaffected: without the flag the platform package installs
+the Tauri host exactly as before.
+
 ## SQLite Migrations
 
 New migrations can be created from the `src-tauri/` directory: