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/models/push_subscription.py

@@ -0,0 +1,20 @@
+from datetime import datetime, timezone
+from sqlalchemy import DateTime, ForeignKey, Integer, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column
+from fabledassistant.models import Base
+
+
+class PushSubscription(Base):
+    __tablename__ = "push_subscriptions"
+    id: Mapped[int] = mapped_column(primary_key=True)
+    user_id: Mapped[int] = mapped_column(Integer, ForeignKey("users.id", ondelete="CASCADE"))
+    endpoint: Mapped[str] = mapped_column(Text)
+    p256dh: Mapped[str] = mapped_column(Text)
+    auth: Mapped[str] = mapped_column(Text)
+    user_agent: Mapped[str | None] = mapped_column(Text, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc))
+    last_used: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+
+    __table_args__ = (
+        UniqueConstraint("user_id", "endpoint", name="uq_push_subscription_user_endpoint"),
+    )