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/demo_server/README.md

@@ -0,0 +1,48 @@
+# Demo server for Play Store screenshots
+
+`tool/screenshots.sh` takes the Play Store screenshots against a **throwaway
+Nextcloud that only contains fake data**, so nothing real can appear in them.
+This folder is that server:
+
+- `docker-compose.yml` - a single Nextcloud container (SQLite, nothing
+  persisted; `docker compose down -v` wipes it).
+- `seed.py` - creates the users and fills them with invented content: landscape
+  "photos" drawn with Pillow, tiny generated PDFs, made-up documents, favorites,
+  shares (to a second user and a public link), trash, a filler file for the
+  storage quota, and edits by a second user so the Activity feed has more than
+  one author. It ends by printing `APP_PASSWORD=...` - an app password for the
+  demo user, so the app can start logged in without the browser login step.
+
+## Running it
+
+Most of the time just run the whole pipeline from the repo root:
+
+```bash
+bash tool/screenshots.sh
+```
+
+(Git Bash is fine on Windows.) You need **Docker**, **Python 3**, **Flutter**
+and an **Android SDK** (`ANDROID_HOME`). Pillow and `requests` are installed
+into `tool/demo_server/.venv` automatically if your Python lacks them. The
+script installs the emulator and a system image through `sdkmanager` on first
+use. Options (`HEADLESS=1`, `DEMO_PORT`, `DEMO_HOST`, `KEEP_SERVER=1`,
+`ANDROID_SERIAL`, ...) are documented at the top of the script.
+
+To poke at the server yourself:
+
+```bash
+docker compose -f tool/demo_server/docker-compose.yml up -d
+python3 tool/demo_server/seed.py          # prints APP_PASSWORD=...
+# browse http://localhost  (Alex / alex-demo-pass, admin / demo-admin-password)
+docker compose -f tool/demo_server/docker-compose.yml down -v
+```
+
+`python3 tool/demo_server/seed.py --generate-only DIR` writes the generated
+files to `DIR` without any server - handy for previewing the fake content.
+
+## Before you upload
+
+Look at every image. The known places where real data could still show up:
+the server address and username (sync header panel, Settings > Accounts), the
+avatar initial, notification icons in the status bar, and anything left over
+from a previously used emulator profile (the script always wipes its own).