feat(#71,#72,#73): SSE push notifications, mention chips, deep-link fixes

- Add SseEmitterRegistry (ConcurrentHashMap, one emitter per user)
- Add GET /api/notifications/stream SSE endpoint and unread-count endpoint
- Push SSE event on every notifyReply / notifyMentions via saveAndPush()
- Collapse V18/V19 migrations into V16 (actor_name + annotation_id upfront)
- Add @Schema(requiredMode=REQUIRED) to NotificationDTO required fields
- Switch NotificationBell from polling to EventSource; seed unread count on open
- Fix MentionEditor: replace setTimeout with await tick(); div role=option
- Add aria-modal=true to NotificationBell dialog
- Tests: SseEmitterRegistryTest (3), NotificationServiceTest (+2), NotificationControllerTest (+5)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/+layout.server.ts

@@ -5,6 +5,8 @@ export const load: LayoutServerLoad = async ({ locals }) => {
 	return {
 		user: locals.user,
 		canWrite: groups.some((g) => g.permissions.includes('WRITE_ALL')),
-		canAnnotate: groups.some((g) => g.permissions.includes('ANNOTATE_ALL'))
+		canAnnotate: groups.some(
+			(g) => g.permissions.includes('WRITE_ALL') || g.permissions.includes('ANNOTATE_ALL')
+		)
 	};
 };