Adds a per-user "Can Stream" permission mirroring the existing "Can Download"
pattern. Server admins can now disable streaming for specific users, encouraging
local downloads instead. Addresses #2572.
Changes:
- User model: stream permission in mapping, defaults, and getter
- ApiKey model: stream permission in defaults
- Controller: 403 enforcement on playback session creation endpoints
- Frontend: permission toggle in admin UI, play button gated by canStream,
download button shown when streaming disabled, message when neither allowed
- Tests: 11 Mocha tests (model + controller), 1 Cypress test (card UI)
- Localization: English strings for toggle label and fallback message
The getter uses !== false (rather than !!) so existing users without the
stream key in their permissions JSON default to allowed on upgrade.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
