feat(swift): Epic 4 - Navigation & Auth compleet

E4.S1 - Login form uitbreiden:
- Interface selector (Swift/Klassiek) toegevoegd
- Visuele keuze met icons (Layout/Zap)
- Redirect naar gekozen interface na login

E4.S2 - Preference opslag:
- updateInterfacePreference() in lib/auth/client.ts
- getInterfacePreference() voor ophalen
- Opslag in user_metadata.preferred_interface

E4.S3 - Redirect middleware:
- /epd → redirect naar preferred interface
- /login → redirect naar preferred interface (als ingelogd)
- Default: klassiek (/epd/clients)

E4.S4 - Fallback Picker:
- FallbackPicker component voor lage confidence
- Grid met 3 opties (Notitie, Zoeken, Overdracht)
- Keyboard shortcuts [1], [2], [3]
- Toont originele input voor context

Voortgang: Epic 4 compleet (8 SP)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/auth/client.ts

@@ -268,3 +268,33 @@ export async function isDemoUser(): Promise<boolean> {
 export async function getDemoAccessLevel(): Promise<'read_only' | 'interactive' | 'presenter' | null> {
   return null
 }
+
+/**
+ * Update user's preferred interface (Swift or Klassiek)
+ * Stored in user_metadata.preferred_interface
+ */
+export type InterfacePreference = 'swift' | 'klassiek'
+
+export async function updateInterfacePreference(preference: InterfacePreference) {
+  const supabase = createClient()
+  const { error } = await supabase.auth.updateUser({
+    data: { preferred_interface: preference }
+  })
+
+  if (error) {
+    console.error('Failed to update interface preference:', error)
+    throw error
+  }
+
+  return true
+}
+
+/**
+ * Get user's preferred interface from metadata
+ * Returns 'klassiek' as default if not set
+ */
+export async function getInterfacePreference(): Promise<InterfacePreference> {
+  const user = await getUser()
+  const preference = user?.user_metadata?.preferred_interface as InterfacePreference | undefined
+  return preference || 'klassiek'
+}