feat: timeline links, network error handling, Tailscale access, mobile fixes

Backend / dev:
- Bind dev server to 0.0.0.0 and allow Tailscale MagicDNS + tailnet-IP origins
  in ALLOWED_HOSTS / CORS / CSRF so the app is reachable over Tailscale
- Unified, idempotent dev launcher (Django + media + shadow watch), hot reload,
  no manual compiles

Frontend:
- Migrate fetches to re-frame :http-xhrio with failure handling; surface
  network / load / save errors where the user expects them
- Extract markdown + link formatting into tl.md: parse/serialize round-trip
  (recursive chip serialization fix), block markdown (headings/lists/paragraphs)
- Timeline-opening links: navigate the stack to any reachable timeline;
  autocomplete lists all timelines (root included, orphans dropped) with a live
  preview that pushes the stack and reverts on commit/cancel
- Annotation pane shows the current context's description with edit-in-context
  (drops into the parent timeline for marks, pops back when done) + root content
- Fixes: deep-link playhead seek, replay-from-end, mobile input zoom, notch
  safe-area insets, autofocus the content field, freeze form to snapshot context

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -17,7 +17,7 @@ python -m venv .venv && .venv/bin/pip install -r requirements.txt
 .venv/bin/python manage.py migrate
 DJANGO_SUPERUSER_PASSWORD=admin .venv/bin/python manage.py createsuperuser --noinput --username admin --email admin@example.com
 .venv/bin/python manage.py seed_demo          # demo project from tl/.../one_two_three.otio
-.venv/bin/python manage.py runserver 9001
+.venv/bin/python manage.py runserver 0.0.0.0:9001   # 0.0.0.0 so it's reachable over Tailscale/LAN
 ```
 
 Admin: <http://127.0.0.1:9001/admin/> (admin / admin). Upload OTIO and inspect