Multi-user sharing, groups, and in-app notifications

Backend:
- Alembic migration 0025: groups, group_memberships, project_shares,
  note_shares, notifications tables
- models: Group, GroupMembership, ProjectShare, NoteShare, Notification
- services/access.py: permission resolution (viewer/editor/admin/owner)
- services/groups.py + routes/groups.py: full group CRUD + membership
- services/sharing.py + routes/shares.py: project/note sharing API
- services/notifications.py: in-app notification create/list/mark-read
- routes/in_app_notifications.py: GET/POST notification endpoints
- routes/users.py: user search endpoint
- services/projects.py + services/notes.py: *_for_user variants
- routes updated to use *_for_user on get/list; adds permission field
- app.py: register all new blueprints

Frontend:
- api/client.ts: ShareEntry, GroupEntry, NotificationEntry types + helpers
- stores/notifications.ts: Pinia store with polling
- NotificationBell.vue: bell icon + badge + dropdown toggle + 60s poll
- NotificationsPanel.vue: unread notification list with mark-all-read
- ShareDialog.vue: teleport modal for sharing projects/notes with users/groups
- SharedWithMeView.vue: /shared route listing shared projects and notes
- AppHeader: NotificationBell, Shared nav link
- ProjectView, NoteViewerView, TaskViewerView: Share button + ShareDialog
- SettingsView: Groups admin tab with create/delete groups + member mgmt
- router: /shared route

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

frontend/src/components/NotificationBell.vue

@@ -0,0 +1,100 @@
+<script setup lang="ts">
+import { ref, onMounted, onUnmounted } from 'vue'
+import { useNotificationsStore } from '@/stores/notifications'
+import NotificationsPanel from './NotificationsPanel.vue'
+
+const store = useNotificationsStore()
+const open = ref(false)
+const wrapRef = ref<HTMLElement | null>(null)
+
+let pollInterval: ReturnType<typeof setInterval> | null = null
+
+function toggle() {
+  open.value = !open.value
+  if (open.value) store.fetchAll()
+}
+
+function close() {
+  open.value = false
+}
+
+function onDocClick(e: MouseEvent) {
+  if (open.value && wrapRef.value && !wrapRef.value.contains(e.target as Node)) {
+    close()
+  }
+}
+
+onMounted(() => {
+  store.fetchCount()
+  pollInterval = setInterval(() => store.fetchCount(), 60_000)
+  document.addEventListener('click', onDocClick, true)
+})
+
+onUnmounted(() => {
+  if (pollInterval) clearInterval(pollInterval)
+  document.removeEventListener('click', onDocClick, true)
+})
+</script>
+
+<template>
+  <div class="bell-wrap" ref="wrapRef">
+    <button
+      class="btn-bell"
+      :class="{ active: open }"
+      @click="toggle"
+      aria-label="Notifications"
+      :title="`${store.count} unread notification${store.count !== 1 ? 's' : ''}`"
+    >
+      <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+        <path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9"/>
+        <path d="M13.73 21a2 2 0 0 1-3.46 0"/>
+      </svg>
+      <span v-if="store.count > 0" class="bell-badge" aria-live="polite">{{ store.count > 99 ? '99+' : store.count }}</span>
+    </button>
+    <NotificationsPanel v-if="open" @close="close" />
+  </div>
+</template>
+
+<style scoped>
+.bell-wrap {
+  position: relative;
+}
+
+.btn-bell {
+  background: none;
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-sm);
+  padding: 0.25rem 0.45rem;
+  cursor: pointer;
+  color: var(--color-text-muted);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  position: relative;
+}
+.btn-bell:hover,
+.btn-bell.active {
+  background: var(--color-bg-card);
+  color: var(--color-text);
+  border-color: var(--color-primary);
+}
+
+.bell-badge {
+  position: absolute;
+  top: -5px;
+  right: -5px;
+  background: var(--color-danger, #ef4444);
+  color: #fff;
+  font-size: 0.6rem;
+  font-weight: 700;
+  min-width: 16px;
+  height: 16px;
+  border-radius: 8px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 0 3px;
+  line-height: 1;
+  pointer-events: none;
+}
+</style>