Add LLM chat integration with streaming responses via Ollama

Phase 4: Full chat system with SSE streaming, note-aware context, and
conversation persistence.

Backend:
- Migration 0005: conversations + messages tables with FKs and indexes
- Conversation/Message SQLAlchemy models with relationships
- LLM service: ensure_model (auto-pull on startup), stream_chat (NDJSON),
  generate_completion, fetch_url_content (HTML stripping), build_context
  (keyword extraction, related note search, URL content injection)
- Chat service: conversation CRUD, save_response_as_note,
  summarize_conversation_as_note
- Chat routes blueprint: 9 endpoints including SSE streaming for messages,
  save/summarize as note, Ollama model listing
- Auto-pull llama3.1 model on app startup (non-blocking)

Frontend:
- apiStreamPost: SSE client using fetch + ReadableStream
- Chat Pinia store with streaming state management
- ChatView: dedicated /chat page with conversation sidebar + message thread
- ChatPanel: slide-out panel with contextNoteId from current route
- ChatMessage: markdown-rendered message bubble with "Save as Note" action
- Updated AppHeader with Chat nav link + panel toggle button
- Updated App.vue to mount ChatPanel with route-derived context
- Added /chat and /chat/:id routes

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

src/fabledassistant/models/__init__.py

@@ -12,3 +12,4 @@ class Base(DeclarativeBase):
 
 
 from fabledassistant.models.note import Note, TaskPriority, TaskStatus  # noqa: E402, F401
+from fabledassistant.models.conversation import Conversation, Message  # noqa: E402, F401

src/fabledassistant/models/conversation.py

@@ -0,0 +1,71 @@
+from datetime import datetime, timezone
+
+from sqlalchemy import DateTime, ForeignKey, Index, Integer, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from fabledassistant.models import Base
+
+
+class Conversation(Base):
+    __tablename__ = "conversations"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    title: Mapped[str] = mapped_column(Text, default="")
+    model: Mapped[str] = mapped_column(Text, default="")
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc),
+    )
+
+    messages: Mapped[list["Message"]] = relationship(
+        back_populates="conversation",
+        cascade="all, delete-orphan",
+        order_by="Message.created_at",
+    )
+
+    def to_dict(self) -> dict:
+        return {
+            "id": self.id,
+            "title": self.title,
+            "model": self.model,
+            "message_count": len(self.messages) if self.messages else 0,
+            "created_at": self.created_at.isoformat(),
+            "updated_at": self.updated_at.isoformat(),
+        }
+
+
+class Message(Base):
+    __tablename__ = "messages"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    conversation_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("conversations.id", ondelete="CASCADE")
+    )
+    role: Mapped[str] = mapped_column(Text)
+    content: Mapped[str] = mapped_column(Text, default="")
+    context_note_id: Mapped[int | None] = mapped_column(
+        Integer, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+
+    conversation: Mapped["Conversation"] = relationship(back_populates="messages")
+
+    __table_args__ = (
+        Index("ix_messages_conversation_id", "conversation_id"),
+    )
+
+    def to_dict(self) -> dict:
+        return {
+            "id": self.id,
+            "conversation_id": self.conversation_id,
+            "role": self.role,
+            "content": self.content,
+            "context_note_id": self.context_note_id,
+            "created_at": self.created_at.isoformat(),
+        }