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/views/ProjectView.vue

@@ -4,6 +4,7 @@ import { useRoute, useRouter } from "vue-router";
 import { apiGet, apiPatch, apiDelete, apiPost } from "@/api/client";
 import { useToastStore } from "@/stores/toast";
 import { relativeTime } from "@/composables/useRelativeTime";
+import ShareDialog from "@/components/ShareDialog.vue";
 
 interface Milestone {
   id: number;
@@ -267,6 +268,7 @@ async function saveProject() {
 }
 
 const showDeleteConfirm = ref(false);
+const showShare = ref(false);
 
 async function confirmDelete() {
   if (!project.value) return;
@@ -294,6 +296,7 @@ async function confirmDelete() {
           <svg viewBox="0 0 24 24" width="14" height="14" fill="currentColor" aria-hidden="true"><path d="M3 13h8V3H3v10zm0 8h8v-6H3v6zm10 0h8V11h-8v10zm0-18v6h8V3h-8z"/></svg>
           Workspace
         </router-link>
+        <button v-if="project" class="btn-share" @click="showShare = true">Share</button>
         <button v-if="project" class="btn-danger-outline" @click="showDeleteConfirm = true">Delete</button>
       </div>
     </div>
@@ -582,6 +585,14 @@ async function confirmDelete() {
         </div>
       </div>
     </teleport>
+
+    <ShareDialog
+      v-if="showShare && project"
+      resource-type="project"
+      :resource-id="project.id"
+      :resource-title="project.title"
+      @close="showShare = false"
+    />
   </main>
 </template>
 
@@ -634,6 +645,19 @@ async function confirmDelete() {
 }
 .btn-workspace:hover { box-shadow: 0 4px 14px rgba(99, 102, 241, 0.42); opacity: 0.95; color: #fff; }
 
+.btn-share {
+  padding: 0.4rem 0.8rem;
+  background: none;
+  border: 1px solid var(--color-border);
+  color: var(--color-text-secondary);
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  font-size: 0.85rem;
+  font-family: inherit;
+  transition: border-color 0.15s, color 0.15s;
+}
+.btn-share:hover { border-color: var(--color-primary); color: var(--color-primary); }
+
 .btn-danger-outline {
   padding: 0.4rem 0.8rem;
   background: none;