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/stores/windows.ts

@@ -3,10 +3,11 @@
 // opened from Knowledge Base, chat, or anywhere else land in the same
 // floating window layer, with several windows open side by side, rather than
 // each page owning its own single-entity sidebar/sheet.
-import { derived, type Readable } from 'svelte/store'
+import { derived, get, type Readable } from 'svelte/store'
 import { createManager, createDesktop, wmStore } from '@surdeddd/wmkit/svelte'
 import { persist } from '@surdeddd/wmkit/persist'
 import { appById, appWindowId } from '$lib/apps'
+import { toggleDocked } from '$lib/stores/docked'
 import { sessions } from '$lib/stores/chat'
 import { heading } from '$lib/tasks'
 
@@ -75,9 +76,18 @@ export function toggleShowDesktop(): void {
 // Opens (or focuses/restores) a registry app's window. Apps are
 // single-instance — double-clicking an already-open app's icon should never
 // stack a second window, same dedupe pattern as openEntityWindow below.
+// Docked apps (e.g. the mascot) have no wmkit window at all — clicking their
+// icon toggles visibility on the Docked Layer instead, so this branches on
+// kind before touching the window manager. All callers (the desktop icon,
+// the taskbar settings button, legacy hash resolution) go through here, so
+// none of them need a kind-specific branch.
 export function openAppWindow(appId: string): void {
-  const app = appById.get(appId)
+  const app = get(appById).get(appId)
   if (!app) return
+  if (app.docked) {
+    toggleDocked(appId)
+    return
+  }
   const id = appWindowId(appId)
   if (wm.get(id)) {
     wm.restore(id)