Rebuild UI on the Noo design system

Replaces the Material 3 screens with the Noo design system: warm
neutrals, one violet accent, pill controls, Schibsted Grotesk/
Instrument Sans, Lucide icons, no gradients/shadows.

- New lib/widgets/noo/ component kit (core, lists, files, media, nav,
  overlays) plus lib/theme/design_tokens.dart for the color/type/space/
  radius/motion tokens.
- Rebuilt the app shell (top/bottom bars, drawer, desktop sidebar and
  toolbar), every tab (Files/Offline, Photos, Favorites, Recent,
  Activity, Trash, Shares), Settings, the lock and login screens, the
  media viewer, search, the details/share sheets, and the share-upload
  and move/copy destination pickers.
- Added a design canvas (linked from DESIGN_SYSTEM.md) covering the
  screens the spec didn't already describe, with matching Android and
  iOS chrome; wrote up the approved recipes into DESIGN_SYSTEM.md §4.
- Removed now-dead legacy widgets (media_grid_tile, swipeable_item,
  sync_status_badge, selectable_thumbnail) and updated
  architecture.md/styling.md/standards.md to describe the new
  structure and component/testing conventions.
- Added widget tests for the noo/ component kit.

This is a UI-only rework: no provider/model/service behavior changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tool/finalize_screenshots.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+"""Makes captured screenshots Play Store ready and reports anything that isn't.
+
+Play wants JPEG or 24-bit PNG (no alpha), each side 320-3840 px, and the long
+side at most twice the short side. The captured PNGs are 32-bit RGBA, so this
+flattens them to RGB in place, then checks the dimensions.
+
+  python3 tool/finalize_screenshots.py store_listing/screenshots
+"""
+import sys
+from pathlib import Path
+
+from PIL import Image
+
+
+def main(directory):
+    files = sorted(Path(directory).glob("*.png"))
+    if not files:
+        sys.exit("No PNGs found in %s" % directory)
+
+    problems = 0
+    for path in files:
+        with Image.open(path) as im:
+            im.load()
+            rgb = Image.new("RGB", im.size, (255, 255, 255))
+            rgb.paste(im, mask=im.getchannel("A") if "A" in im.getbands() else None)
+        rgb.save(path, "PNG", optimize=True)
+
+        w, h = rgb.size
+        notes = []
+        if min(w, h) < 320 or max(w, h) > 3840:
+            notes.append("side outside 320-3840 px")
+        if max(w, h) > 2 * min(w, h):
+            notes.append("aspect ratio over 2:1")
+        problems += bool(notes)
+        print("%-32s %4dx%-4d %s" % (path.name, w, h, "; ".join(notes) or "ok"))
+
+    print("\n%d screenshots, %d with problems" % (len(files), problems))
+    sys.exit(1 if problems else 0)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1] if len(sys.argv) > 1 else "store_listing/screenshots")