fix: avatar stale state, nginx intercept, and dev tooling

Frontend (SettingsPage):
- Sync avatarUrl state via useEffect when me.avatar_url changes after
  background refetch, so profile section never shows stale avatar
- Invalidate ["comments"] after upload/generate/remove so SongPage
  comment avatars update immediately instead of waiting for staleTime
- Fix Remove button: was sending avatar_url: undefined which JSON.stringify
  drops entirely, so the server never cleared it; now sends ""

nginx:
- Change /api/ and /ws/ locations to use ^~ prefix so the static-asset
  regex rule (~* \.(png|svg|ico)$) cannot intercept API paths; PNG/SVG
  avatar uploads were returning 404 from nginx in production
- Merge nc-scan 300s timeout into ^~ /api/v1/bands/ block
- Add client_max_body_size 10m (default 1MB was silently rejecting
  uploads before they reached FastAPI)

Dev tooling:
- Add docker-compose.dev.yml for hot-reload development workflow
- Add Taskfile.yml with dev, test, lint, migrate, and shell tasks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -0,0 +1,17 @@
+services:
+  api:
+    build:
+      context: ./api
+      target: development
+    volumes:
+      - ./api/src:/app/src
+    ports:
+      - "8000:8000"
+
+  audio-worker:
+    volumes:
+      - ./worker/src:/app/src
+
+  nc-watcher:
+    volumes:
+      - ./watcher/src:/app/src