fix: unify theme system - fix theme switching persistence

- Unified localStorage key to 'theme-preference' across all components
- Fixed header.tsx using wrong localStorage key ('theme' instead of 'theme-preference')
- Added localStorage hybrid persistence for instant theme changes
- Removed router.refresh() which was causing stale data revert
- Replaced Blue theme with Sepia
- Consolidated auth() calls to prevent race conditions
- Updated UserSettingsData types to include all themes

_bmad-output/design-proposals/design-simplification-proposal.md

@@ -213,7 +213,7 @@ export function NoteActionMenu({
   note={note}
   onTogglePin={handleTogglePin}
   onMoveToNotebook={handleMoveToNotebook}
-  onSetReminder={() => {/* TODO */}}
+  onSetReminder={() => {/* Ouvrir le dialog de rappel - à implémenter */}}
   onShowConnections={() => setShowConnectionsOverlay(true)}
   onArchive={handleToggleArchive}
   onDelete={handleDelete}