feat(rag): RAG scoping and context isolation controls

- Migration 0030: add conversations.rag_project_id (NULL=orphan-only,
  -1=all notes, positive=project), projects.auto_summary and
  projects.summary_updated_at
- Three-value scope semantics thread from build_context() → semantic
  search and keyword fallback via orphan_only + effective_project_id
- Project summarization background job (generate_project_summary,
  backfill_project_summaries) called via Ollama; triggered on project
  update and note saves (debounced 1h); runs at startup
- New LLM tools: search_projects (SequenceMatcher scoring on
  title+description+auto_summary) and set_rag_scope (persists to DB,
  workspace-guarded, emits new_rag_scope in SSE done event)
- execute_tool() accepts conv_id + workspace_project_id; generation_task
  passes both and captures scope changes for SSE done enrichment
- Frontend: Conversation type gets rag_project_id; chat store adds
  ragProjectId computed + updateRagScope(); SSE done handler syncs scope
- ChatView: replace sidebar ProjectSelector with a scope chip pill above
  the input bar, animated dropdown, pulse on model-driven scope change

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

src/fabledassistant/models/conversation.py

@@ -23,6 +23,8 @@ class Conversation(Base, TimestampMixin):
     conversation_type: Mapped[str] = mapped_column(Text, default="chat", server_default="chat")
     # For briefing conversations only: the calendar date this briefing covers.
     briefing_date: Mapped[datetime.date | None] = mapped_column(Date, nullable=True)
+    # NULL = orphan notes only; -1 = all notes; positive int = specific project
+    rag_project_id: Mapped[int | None] = mapped_column(Integer, nullable=True, default=None)
 
     messages: Mapped[list["Message"]] = relationship(
         back_populates="conversation",
@@ -47,6 +49,7 @@ class Conversation(Base, TimestampMixin):
             "model": self.model,
             "conversation_type": self.conversation_type,
             "briefing_date": self.briefing_date.isoformat() if self.briefing_date else None,
+            "rag_project_id": self.rag_project_id,
             "message_count": msg_count,
             "created_at": self.created_at.isoformat(),
             "updated_at": self.updated_at.isoformat(),