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.

crates-tauri/yaak-app-client/src/models_ext.rs

@@ -147,7 +147,7 @@ pub(crate) fn models_upsert<R: Runtime>(
     let db = window.db();
     let blobs = window.blob_manager();
     let source = &UpdateSource::from_window_label(window.label());
-    yaak::models_ops::upsert_model(&db, &blobs, model, source)
+    yaak_models::models_ops::upsert_model(&db, &blobs, model, source)
 }
 
 // Async so cascading deletes (e.g. a workspace with thousands of requests) run on a
@@ -163,7 +163,7 @@ pub(crate) async fn models_delete<R: Runtime>(
         // Use transaction for deletions because it might recurse
         window.with_tx(|tx| {
             let source = &UpdateSource::from_window_label(window.label());
-            yaak::models_ops::delete_model(tx, &blobs, model, source)
+            yaak_models::models_ops::delete_model(tx, &blobs, model, source)
         })
     })
     .await
@@ -178,7 +178,7 @@ pub(crate) fn models_duplicate<R: Runtime>(
     // Use transaction for duplications because it might recurse
     window.with_tx(|tx| {
         let source = &UpdateSource::from_window_label(window.label());
-        yaak::models_ops::duplicate_model(tx, &model_type, &model_id, source)
+        yaak_models::models_ops::duplicate_model(tx, &model_type, &model_id, source)
     })
 }