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/services/llm.py

@@ -536,12 +536,18 @@ async def build_context(
     # (score, note) pairs — score is float for semantic results, None for keyword fallback.
     found_scored: list[tuple[float | None, object]] = []
 
+    # Derive scope flags from rag_project_id three-value semantics:
+    # None → orphan notes only; -1 → all notes; positive int → that project
+    orphan_only = rag_project_id is None
+    effective_project_id = rag_project_id if (rag_project_id is not None and rag_project_id != -1) else None
+
     # Try semantic search first; fall back to keyword search on failure / no results.
     try:
         from fabledassistant.services.embeddings import semantic_search_notes
         for score, note in await semantic_search_notes(
             user_id, user_message, exclude_ids=search_exclude or None, limit=8,
-            project_id=rag_project_id,
+            project_id=effective_project_id,
+            orphan_only=orphan_only,
         ):
             found_scored.append((score, note))
     except Exception:
@@ -553,7 +559,8 @@ async def build_context(
             try:
                 for note in await search_notes_for_context(
                     user_id, keywords, exclude_ids=search_exclude or None, limit=8,
-                    project_id=rag_project_id,
+                    project_id=effective_project_id,
+                    orphan_only=orphan_only,
                 ):
                     found_scored.append((None, note))
             except Exception: