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.

apps/yaak-client/commands/openSettings.tsx

@@ -1,3 +1,4 @@
+import { platform } from "@yaakapp-internal/platform";
 import type { SettingsTab } from "../components/Settings/Settings";
 import { activeWorkspaceIdAtom } from "../hooks/useActiveWorkspace";
 import { createFastMutation } from "../hooks/useFastMutation";
@@ -14,11 +15,19 @@ export const openSettings = createFastMutation<void, string, SettingsTabWithSubt
     const workspaceId = jotaiStore.get(activeWorkspaceIdAtom);
     if (workspaceId == null) return;
 
-    const location = router.buildLocation({
-      to: "/workspaces/$workspaceId/settings",
-      params: { workspaceId },
-      search: { tab: (tab ?? undefined) as SettingsTab | undefined },
-    });
+    const to = "/workspaces/$workspaceId/settings" as const;
+    const params = { workspaceId };
+    const search = { tab: (tab ?? undefined) as SettingsTab | undefined };
+
+    // Settings is its own window where the host has windows to give. Where it
+    // doesn't — a browser tab — the same route opens in place, which is the
+    // whole difference: it is already a route, not a separate app.
+    if (!platform.capabilities.multiWindow) {
+      await router.navigate({ to, params, search });
+      return;
+    }
+
+    const location = router.buildLocation({ to, params, search });
 
     await rpc("cmd_new_child_window", {
       url: location.href,

apps/yaak-client/commands/switchWorkspace.tsx

@@ -1,3 +1,4 @@
+import { platform } from "@yaakapp-internal/platform";
 import { createFastMutation } from "../hooks/useFastMutation";
 import { getRecentCookieJars } from "../hooks/useRecentCookieJars";
 import { getRecentEnvironments } from "../hooks/useRecentEnvironments";
@@ -24,7 +25,9 @@ export const switchWorkspace = createFastMutation<
       request_id: requestId,
     };
 
-    if (inNewWindow) {
+    // A host without windows opens the workspace here instead. Refusing would
+    // strand the user on the workspace they were trying to leave.
+    if (inNewWindow && platform.capabilities.multiWindow) {
       const location = router.buildLocation({
         to: "/workspaces/$workspaceId",
         params: { workspaceId },

apps/yaak-client/vite.config.ts

@@ -17,9 +17,37 @@ const standardFontsDir = normalizePath(
   path.join(path.dirname(require.resolve("pdfjs-dist/package.json")), "standard_fonts"),
 );
 
+/**
+ * Which host the platform package installs. `web` builds Yaak to run in a plain
+ * browser tab, with its own IndexedDB store instead of the Rust engine; anything
+ * else builds the desktop app exactly as before.
+ */
+const yaakTarget = process.env.YAAK_TARGET === "web" ? "web" : "desktop";
+
 // https://vitejs.dev/config/
 export default defineConfig(async () => {
   return {
+    resolve: {
+      alias:
+        yaakTarget === "web"
+          ? {
+              // Resolve the platform package to its browser entry, so a web
+              // build never pulls `@tauri-apps/*` into the graph at all. A
+              // build-time branch inside the package would not manage that:
+              // the dead branch folds away, but the imports it guarded stay.
+              "@yaakapp-internal/platform": path.resolve(
+                import.meta.dirname,
+                "../../packages/platform/src/index.web.ts",
+              ),
+            }
+          : {},
+    },
+    // The browser host runs the model layer in a worker; that bundle needs the
+    // same wasm and top-level-await handling as the main one.
+    worker: {
+      format: "es" as const,
+      plugins: () => [wasm(), topLevelAwait()],
+    },
     plugins: [
       wasm(),
       tanstackRouter({