Add multi-user auth, background generation, and chat UX improvements

Phase 5: Multi-user authentication with session cookies, bcrypt passwords,
first-user-is-admin pattern, per-user data isolation, backup/restore,
Docker Swarm production stack with secrets and network isolation.

Phase 5.1: Chat UX improvements:
- Background generation architecture (GenerationBuffer + asyncio task)
  with SSE fan-out, reconnect support, and periodic DB flushes
- LLM-generated conversation titles (first exchange + every 10th message)
- Stop generation button with cancel_event and partial content preservation
- Relative timestamps in sidebar (5m ago, 3h ago, then dates)
- Empty chat auto-cleanup on navigation away
- Save-as-note uses LLM for title generation, tags notes with "chat"
- Summarize-as-note also tags with "chat"

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

src/fabledassistant/models/conversation.py

@@ -11,6 +11,9 @@ class Conversation(Base):
     __tablename__ = "conversations"
 
     id: Mapped[int] = mapped_column(primary_key=True)
+    user_id: Mapped[int | None] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=True
+    )
     title: Mapped[str] = mapped_column(Text, default="")
     model: Mapped[str] = mapped_column(Text, default="")
     created_at: Mapped[datetime] = mapped_column(
@@ -30,6 +33,7 @@ class Conversation(Base):
 
     __table_args__ = (
         Index("ix_conversations_updated_at", "updated_at"),
+        Index("ix_conversations_user_id", "user_id"),
     )
 
     def to_dict(self) -> dict:
@@ -57,6 +61,7 @@ class Message(Base):
     )
     role: Mapped[str] = mapped_column(Text)
     content: Mapped[str] = mapped_column(Text, default="")
+    status: Mapped[str] = mapped_column(Text, default="complete")
     context_note_id: Mapped[int | None] = mapped_column(
         Integer, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
     )
@@ -76,6 +81,7 @@ class Message(Base):
             "conversation_id": self.conversation_id,
             "role": self.role,
             "content": self.content,
+            "status": self.status,
             "context_note_id": self.context_note_id,
             "created_at": self.created_at.isoformat(),
         }