feat(web): app-registry architecture — OS + Apps, lazy loading, installable apps

Problem: the frontend had an implicit OS+Apps metaphor (desktop, floating
windows, an app registry) but the contract was informal — the mascot was
hardcoded into the shell, all apps were statically imported into one
800KB bundle, and there was no install/uninstall path.

Change: three phases landed.
- Phase 1 (contract + docked kind): AppDef extended with docked/noIcon
  and optional geometry; the mascot registered as a docked app via a
  generic DockedLayer that replaces the hardcoded <MascotLayer />;
  openAppWindow branches on docked → toggleDocked; persisted docked
  visibility store (absent key = visible, no APPS import to avoid a
  static cycle).
- Phase 2 (lazy loading): AppDef.component is now a dynamic-import
  loader; LazyApp renders with a loading skeleton; Vite code-splits
  each app (main bundle 800KB→485KB); the LazyMascot wrapper is gone
  since the lazy loader breaks the import cycle directly.
- Phase 3 (installable apps, local bundles): AppManifest + catalog +
  installApp/uninstallApp + localStorage persistence; reactive apps
  store (built-in + installed) and derived appById; App Store page;
  Notes demo app; icons.ts and WindowLayer's orphan-close react to
  registration so installs appear without a reload.
- Structure: data-table casing unified to PascalCase; the mislabeled
  DataTable.svelte.ts (pure types, not runes) renamed to types.ts;
  LazyApp colocated with its desktop-shell consumers; app-store moved
  under lib/ so the dependency direction is consistent.

Risk: the app registry is now a reactive store, not a static array, so
every consumer (Desktop, DockedLayer, Taskbar, icons, windows) reads
from derived stores. Two static-cycle traps are documented in
docs/mbse/components.md §9: docked.ts must not import APPS (it would
fire a TDZ at init via the apps.ts→pages→windows.ts→here path), and
apps.ts must not statically import the mascot (the lazy loader defers
its module graph). Remote bundle loading, the /api/v1/apps endpoint,
and permission enforcement are deliberately NOT in this commit — they
are security-critical and deferred to Phase 4 with an ADR.

Verification: vitest 38/38; svelte-check + tsc clean for changed files;
eslint clean; vite build green; runtime smoke confirmed (install
Notes → icon appears → open → uninstall → icon + window gone; survives
reload). docs/mbse/components.md Component 9 and the plan updated.

Plan: plans/2026-07-21-frontend-os-apps-architecture.md

web/src/lib/app-store/apps/Notes.svelte

@@ -0,0 +1,57 @@
+<script lang="ts">
+  // Notes — a trivial installable app demoing the App Store lifecycle.
+  // Installed from the App Store, gets a desktop icon, opens in a window,
+  // has its own localStorage-backed state, and uninstalls cleanly. No
+  // shell-internal imports — this is a self-contained app that could be
+  // shipped as a standalone bundle (Phase 4 will load such bundles from
+  // a URL; here it's bundled and discovered via the catalog).
+  let { storageKey = 'oikos-app-notes' }: { storageKey?: string } = $props()
+
+  let text = $state('')
+  let saved = $state(false)
+
+  function load(): string {
+    if (typeof localStorage === 'undefined') return ''
+    return localStorage.getItem(storageKey) ?? ''
+  }
+  function save(): void {
+    if (typeof localStorage === 'undefined') return
+    localStorage.setItem(storageKey, text)
+    saved = true
+    setTimeout(() => (saved = false), 1500)
+  }
+
+  function onKeydown(e: KeyboardEvent) {
+    if ((e.metaKey || e.ctrlKey) && e.key.toLowerCase() === 's') {
+      e.preventDefault()
+      save()
+    }
+  }
+
+  text = load()
+  $effect(() => {
+    if (!text) return
+    const t = setTimeout(() => save(), 2000)
+    return () => clearTimeout(t)
+  })
+</script>
+
+<div class="flex h-full min-h-0 flex-col gap-2 p-4">
+  <div class="flex shrink-0 items-center justify-between">
+    <h2 class="text-sm font-medium">Notes</h2>
+    <span class="text-xs text-muted-foreground">
+      {#if saved}saved{:else}unsaved{/if}
+    </span>
+  </div>
+  <textarea
+    bind:value={text}
+    onkeydown={onKeydown}
+    placeholder="Type here. Auto-saves 2s after you stop, or Cmd/Ctrl+S."
+    class="min-h-0 flex-1 resize-none rounded-md border bg-background p-3 font-mono text-sm leading-relaxed focus-visible:outline-2 focus-visible:outline-ring"
+  ></textarea>
+  <p class="shrink-0 text-xs text-muted-foreground">
+    A demo installable app — uninstall it from the App Store to remove its
+    icon and window. Its notes persist in localStorage under
+    <code class="font-mono">{storageKey}</code>.
+  </p>
+</div>