feat: centralize identity creation with router navigation guard

Migrate automatic identity creation from scattered view components to centralized
router navigation guard for consistent behavior across all entry points.

**Key Changes:**
- Add global beforeEach navigation guard in router/index.ts
- Remove automatic identity creation from HomeView, ContactsView, InviteOneAcceptView,
  and OnboardMeetingMembersView
- Keep minimal fallback logic in deep link scenarios with logging
- Exclude manual identity creation routes (/start, /new-identifier, /import-account)

**Benefits:**
- Eliminates code duplication and race conditions
- Ensures consistent identity creation regardless of entry point
- Centralizes error handling with fallback to manual creation
- Improves maintainability with single point of change

**Files Modified:**
- src/router/index.ts: Add navigation guard with identity creation logic
- src/views/HomeView.vue: Remove automatic creation, simplify initializeIdentity()
- src/views/ContactsView.vue: Add fallback with logging
- src/views/InviteOneAcceptView.vue: Add fallback with logging
- src/views/OnboardMeetingMembersView.vue: Add fallback with logging

**Testing:**
- Verified first-time user navigation creates identity automatically
- Confirmed existing users bypass creation logic
- Validated manual creation routes remain unaffected
- Tested deep link scenarios with fallback logic

**Documentation:**
- Created docs/identity-creation-migration.md with comprehensive details
- Includes migration rationale, implementation details, testing scenarios
- Documents security considerations and rollback plan

Resolves inconsistent identity creation behavior across different app entry points.

src/views/OnboardMeetingMembersView.vue

@@ -111,7 +111,11 @@ export default class OnboardMeetingMembersView extends Vue {
     this.firstName = settings?.firstName || "";
     this.isRegistered = !!settings?.isRegistered;
     try {
+      // Identity creation should be handled by router guard, but keep as fallback for meeting setup
       if (!this.activeDid) {
+        logger.info(
+          "[OnboardMeetingMembersView] No active DID found, creating identity as fallback for meeting setup",
+        );
         this.activeDid = await generateSaveAndActivateIdentity();
         this.isRegistered = false;
       }