fix: use CALDAV_ENABLED for calendar feature flag (#1070)

* fix: add FF_ENABLE_CALDAV feature flag for CalDAV functionality

Introduces a new dedicated feature flag for CalDAV sync that checks
both FF_ENABLE_CALDAV and CALDAV_ENABLED environment variables. This
allows the CalDAV tab to appear in profile settings when users set
CALDAV_ENABLED=true as documented.

The existing FF_ENABLE_CALENDAR remains unchanged as it's for a
separate (hidden) calendar feature.

Changes:
- Added 'caldav' feature flag to backend service (checks FF_ENABLE_CALDAV
  or CALDAV_ENABLED)
- Updated frontend FeatureFlags interface to include 'caldav'
- Changed CalDAV tab to use 'caldav' feature flag instead of 'calendar'
- Added FF_ENABLE_CALDAV to .env.example, .env.test, Dockerfile, and CI

Fixes #1048

* fix: add caldav property to all FeatureFlags initializations

Fixes TypeScript errors where FeatureFlags objects were missing the
new caldav property in:
- frontend/utils/featureFlags.ts (defaultFlags and error return)
- frontend/components/Navbar.tsx
- frontend/components/Sidebar.tsx
- frontend/components/Sidebar/SidebarNav.tsx

.github/workflows/ci.yml

@@ -33,6 +33,7 @@ jobs:
       run: npm run backend:test
       env:
         FF_ENABLE_BACKUPS: 'true'
+        FF_ENABLE_CALDAV: 'true'
         FF_ENABLE_CALENDAR: 'true'
 
     - name: Build frontend