Add Projects, Milestones, RAG auto-inject, push notifications, PWA, tag normalisation

## Projects & Milestones (Phases A + G)
- New models: Project, Milestone (Project → Milestone → Task hierarchy)
- notes table: project_id + milestone_id FKs; parent_id FK constraint activated
- Migrations: 0017 (projects), 0018 (push_subscriptions), 0019 (events), 0020 (milestones)
- Services: projects.py, milestones.py (CRUD + progress tracking)
- Routes: /api/projects + /api/projects/<id>/milestones
- LLM tools: create/list/get/update project; create/list milestone; project + milestone + parent_task params on note/task tools
- Frontend: ProjectListView (stacked milestone bars), ProjectView (milestone-grouped kanban), ProjectSelector, MilestoneSelector, NoteEditorView + TaskEditorView updated

## RAG Auto-injection (Phase B)
- Notes ≥0.60 cosine similarity auto-injected into system prompt (max 3, 800 chars each)
- excluded_note_ids param; ChatView "Auto-included" sidebar section

## Summarisation improvements (Phase C)
- Threshold 20→30, keep-recent 6→8, max_tokens 200→400
- Two-pass summarisation for histories >50 messages

## Browser push notifications (Phase E)
- PushSubscription model + migration; pywebpush dependency
- /api/push routes; VAPID config; fire-and-forget on generation complete
- Frontend: sw.js, push store, Settings toggle

## PWA manifest (Phase F)
- manifest.json, Apple meta tags, service worker registration in main.ts

## Tag normalisation
- All tags lowercased + deduplicated at backend (create_note/update_note) and frontend (TagInput sanitize)
- Note/Task types gain project_id + milestone_id fields; store signatures updated

## CalDAV
- Radicale embedded server reverted; back to user-configured external CalDAV

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

src/fabledassistant/services/caldav.py

@@ -16,13 +16,13 @@ CALDAV_SETTING_KEYS = ["caldav_url", "caldav_username", "caldav_password", "cald
 
 
 async def get_caldav_config(user_id: int) -> dict[str, str]:
-    """Read CalDAV settings for the given user."""
+    """Return the user's CalDAV config from their settings."""
     all_settings = await get_all_settings(user_id)
     return {k: all_settings.get(k, "") for k in CALDAV_SETTING_KEYS}
 
 
 async def is_caldav_configured(user_id: int) -> bool:
-    """Check if CalDAV URL, username, and password are all set."""
+    """Check if the user has configured an external CalDAV server."""
     config = await get_caldav_config(user_id)
     return bool(config.get("caldav_url") and config.get("caldav_username") and config.get("caldav_password"))
 
@@ -55,8 +55,8 @@ def _make_client(config: dict[str, str]) -> caldav.DAVClient:
     """Create a CalDAV client from config dict."""
     return caldav.DAVClient(
         url=config["caldav_url"],
-        username=config["caldav_username"],
-        password=config["caldav_password"],
+        username=config.get("caldav_username") or None,
+        password=config.get("caldav_password") or None,
     )
 
 
@@ -158,8 +158,8 @@ def _add_attendees(event: icalendar.Event, attendees: list[str]) -> None:
 
 def _check_config(config: dict[str, str]) -> None:
     """Raise if CalDAV is not configured."""
-    if not (config.get("caldav_url") and config.get("caldav_username") and config.get("caldav_password")):
-        raise ValueError("CalDAV is not configured. Go to Settings -> Calendar to set it up.")
+    if not config.get("caldav_url"):
+        raise ValueError("CalDAV is not configured. Go to Settings → Calendar to enter your server URL.")
 
 
 async def create_event(
@@ -707,8 +707,8 @@ async def delete_todo(
 async def test_connection(user_id: int) -> dict:
     """Test the CalDAV connection and return status."""
     config = await get_caldav_config(user_id)
-    if not (config.get("caldav_url") and config.get("caldav_username") and config.get("caldav_password")):
-        return {"success": False, "error": "CalDAV is not configured. Please fill in URL, username, and password."}
+    if not config.get("caldav_url"):
+        return {"success": False, "error": "CalDAV is not configured."}
 
     def _test():
         client = _make_client(config)