Add invitation system, table of contents, actionable dashboard, and settings improvements

Invitation system (Phase 5.7):
- invitation_tokens table (migration 0012) with SHA256-hashed tokens, 7-day expiry
- Admin CRUD endpoints: POST/GET/DELETE /api/admin/invitations
- Branded invitation email with registration link
- /register-invite frontend view with token validation and account creation
- Admin UI: invite form + pending invitations table with revoke
- Configurable base URL setting for email links (replaces hardcoded Config.BASE_URL)

Table of contents + markdown improvements (Phase 5.8):
- TableOfContents component: sticky sidebar, heading parsing, smooth-scroll
- Custom marked renderer adds id attributes to headings for anchor links
- stripFirstLineTags() prevents leading #tags from rendering as headings
- NoteViewerView/TaskViewerView flex layout with TOC sidebar (hidden ≤1200px)
- Model catalog refresh: added llama3.2/3.3, gemma3, qwen3, phi4, deepseek-r1,
  qwen2.5-coder, dolphin3; added Reasoning category; removed discontinued models
- Settings model section split into Installed/Available tabs

Actionable dashboard (Phase 5.9):
- due_before/due_after query params on /api/tasks (exclusive < / inclusive >=)
- HomeView rewritten: overdue (red accent), due today, in progress, chats, notes
- 5 parallel API calls via Promise.allSettled
- Client-side done filtering and in-progress deduplication
- Task sections hidden when empty; status toggle removes done tasks

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

src/fabledassistant/routes/tasks.py

@@ -29,6 +29,11 @@ async def list_tasks_route():
     limit = request.args.get("limit", 50, type=int)
     offset = request.args.get("offset", 0, type=int)
 
+    due_before_str = request.args.get("due_before")
+    due_after_str = request.args.get("due_after")
+    due_before = date.fromisoformat(due_before_str) if due_before_str else None
+    due_after = date.fromisoformat(due_after_str) if due_after_str else None
+
     tasks, total = await list_notes(
         uid,
         q=q,
@@ -36,6 +41,8 @@ async def list_tasks_route():
         is_task=True,
         status=status,
         priority=priority,
+        due_before=due_before,
+        due_after=due_after,
         sort=sort,
         order=order,
         limit=limit,