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

frontend/components/Navbar.tsx

@@ -42,6 +42,7 @@ const Navbar: React.FC<NavbarProps> = ({
     const [featureFlags, setFeatureFlags] = useState<FeatureFlags>({
         backups: false,
         calendar: false,
+        caldav: false,
         habits: false,
         mcp: false,
     });

frontend/components/Profile/ProfileSettings.tsx

@@ -144,6 +144,7 @@ const ProfileSettings: React.FC<ProfileSettingsProps> = ({
     const [featureFlags, setFeatureFlags] = useState<FeatureFlags>({
         backups: false,
         calendar: false,
+        caldav: false,
         habits: false,
         mcp: false,
     });
@@ -1174,7 +1175,7 @@ const ProfileSettings: React.FC<ProfileSettingsProps> = ({
             id: 'caldav',
             name: t('profile.tabs.caldav', 'CalDAV Sync'),
             icon: <CalendarIcon className="w-5 h-5" />,
-            featureFlag: 'calendar',
+            featureFlag: 'caldav',
         },
         {
             id: 'mcp',

frontend/components/Sidebar.tsx

@@ -56,6 +56,7 @@ const Sidebar: React.FC<SidebarProps> = ({
     const [featureFlags, setFeatureFlags] = useState<FeatureFlags>({
         backups: false,
         calendar: false,
+        caldav: false,
         habits: false,
         mcp: false,
     });

frontend/components/Sidebar/SidebarNav.tsx

@@ -30,6 +30,7 @@ const SidebarNav: React.FC<SidebarNavProps> = ({
     const [featureFlags, setFeatureFlags] = useState<FeatureFlags>({
         backups: false,
         calendar: false,
+        caldav: false,
         habits: false,
         mcp: false,
     });

frontend/utils/featureFlags.ts

@@ -3,6 +3,7 @@ import { getApiPath } from '../config/paths';
 export interface FeatureFlags {
     backups: boolean;
     calendar: boolean;
+    caldav: boolean;
     habits: boolean;
     mcp: boolean;
 }
@@ -24,6 +25,7 @@ export const getFeatureFlags = async (): Promise<FeatureFlags> => {
             return {
                 backups: false,
                 calendar: false,
+                caldav: false,
                 habits: false,
                 mcp: false,
             };
@@ -33,6 +35,7 @@ export const getFeatureFlags = async (): Promise<FeatureFlags> => {
         const defaultFlags: FeatureFlags = {
             backups: false,
             calendar: false,
+            caldav: false,
             habits: false,
             mcp: false,
         };
@@ -46,6 +49,7 @@ export const getFeatureFlags = async (): Promise<FeatureFlags> => {
         return {
             backups: false,
             calendar: false,
+            caldav: false,
             habits: false,
             mcp: false,
         };