Add LLM tool calling for creating tasks, notes, and searching from chat

Ollama tool/function calling integration allows the LLM to create tasks,
create notes, and search existing notes on behalf of the user during chat.
Multi-round tool loop (max 5 rounds) lets the model execute tools then
produce a natural language response. Tool results are persisted in a new
JSONB column on messages and rendered as compact cards with linked titles.

- Migration 0013: add tool_calls JSONB column to messages
- New services/tools.py: tool definitions + execute_tool dispatcher
- llm.py: ChatChunk dataclass, stream_chat_with_tools(), date in system prompt
- generation_task.py: multi-round tool call loop with SSE tool_call events
- Frontend: ToolCallRecord type, streamingToolCalls in store, ToolCallCard
  component, rendering in ChatMessage and ChatView streaming bubble

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

src/fabledassistant/models/conversation.py

@@ -2,6 +2,7 @@ from datetime import datetime, timezone
 
 from sqlalchemy import DateTime, ForeignKey, Index, Integer, Text
 from sqlalchemy import inspect
+from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from fabledassistant.models import Base
@@ -65,6 +66,7 @@ class Message(Base):
     context_note_id: Mapped[int | None] = mapped_column(
         Integer, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
     )
+    tool_calls: Mapped[list | None] = mapped_column(JSONB, nullable=True)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
@@ -83,5 +85,6 @@ class Message(Base):
             "content": self.content,
             "status": self.status,
             "context_note_id": self.context_note_id,
+            "tool_calls": self.tool_calls,
             "created_at": self.created_at.isoformat(),
         }