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>

index.html

@@ -3,7 +3,10 @@
   <head>
     <meta charset="UTF-8" />
     <link rel="icon" type="image/x-icon" href="/favicon.ico" />
+    <link rel="apple-touch-icon" href="/pwa-icon-192.png" />
+    <link rel="manifest" href="/manifest.webmanifest" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="theme-color" content="#17171b" />
     <title>RUWIO</title>
   </head>
   <body>