0.12.0: document drawer redesign, PWA install, clip/audio context menus + push-cascade

- Document drawer slides out from under the topbar (no tab, no hover
  peek); opens via project-name button, closes on outside-click or ESC.
  Layout: inputs row + divider + preset row, presets user-managed via
  popup and persisted in localStorage.
- PWA manifest + minimal service worker so Chrome installs RUWIO as a
  standalone app — suppresses the native fullscreen exit overlay.
- Clips and audio clips get right-click context menus (Duplicate /
  Delete) via new `duplicateClipInstance` / `duplicateAudioClip` store
  actions.
- Clip moves cascade non-overlap in both directions; `setAudioClipPosition`
  now pushes backward as well as forward. New `setClipInstancePosition`
  gives clip instances the same behaviour.
- Library drags carry timeline-shaped ghost previews (audio pill, clip
  pill, button thumb) instead of the library row; clip lane renders a
  dashed drop-target ghost and rejects window-overlap drops.
- Scene / Clipart drawer tabs disappear in fullscreen; the 24 px they
  occupied is reclaimed for the stage. Play button sits on the exact
  horizontal center via a 3-column grid in the transport cluster.
- Tests: context menu + push-cascade + duplicate action coverage for
  both clip kinds; DocumentDrawer suite rewritten for the slide-out
  model.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

public/manifest.webmanifest

@@ -0,0 +1,32 @@
+{
+  "name": "RUWIO",
+  "short_name": "RUWIO",
+  "description": "A timeline-based animation editor that runs in your browser.",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "display_override": ["window-controls-overlay", "standalone"],
+  "orientation": "any",
+  "background_color": "#17171b",
+  "theme_color": "#17171b",
+  "icons": [
+    {
+      "src": "/pwa-icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "/pwa-icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "/pwa-icon-maskable-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    }
+  ]
+}

public/sw.js

@@ -0,0 +1,19 @@
+// Minimal service worker. Present so Chrome considers the site
+// installable as a PWA; installed instances run in standalone display
+// mode, which removes the top-edge "exit fullscreen" indicator that
+// regular-browser tabs get when entering the Fullscreen API.
+// No caching logic — assets are served straight from the network so
+// a new build is picked up without a version bump dance.
+
+self.addEventListener('install', (event) => {
+  self.skipWaiting()
+})
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(self.clients.claim())
+})
+
+self.addEventListener('fetch', () => {
+  // Fall through to network. Required handler for installability; we
+  // deliberately do nothing else so dev/prod behave identically.
+})