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>

frontend/src/stores/chat.ts

@@ -75,6 +75,17 @@ export const useChatStore = defineStore("chat", () => {
   const streamingPendingTool = computed(() => convStreams.value[currentConversation.value?.id ?? 0]?.pendingTool ?? null);
   const lastContextMeta = computed(() => convStreams.value[currentConversation.value?.id ?? 0]?.contextMeta ?? null);
 
+  const ragProjectId = computed<number | null>(
+    () => currentConversation.value?.rag_project_id ?? null
+  );
+
+  async function updateRagScope(convId: number, ragProjectId: number | null): Promise<void> {
+    await apiPatch(`/api/chat/conversations/${convId}`, { rag_project_id: ragProjectId });
+    if (currentConversation.value?.id === convId) {
+      currentConversation.value.rag_project_id = ragProjectId;
+    }
+  }
+
   function isStreamingConv(id: number): boolean {
     return convStreams.value[id]?.streaming ?? false;
   }
@@ -387,6 +398,10 @@ export const useChatStore = defineStore("chat", () => {
               };
               if (currentConversation.value?.id === convId) {
                 currentConversation.value.messages.push(assistantMsg);
+                // Update RAG scope if the model changed it mid-conversation
+                if (event.data.new_rag_scope !== undefined) {
+                  currentConversation.value.rag_project_id = event.data.new_rag_scope as number | null;
+                }
               }
               // Update updated_at only — message_count was already incremented at send time
               const idx = conversations.value.findIndex((c) => c.id === convId);
@@ -594,6 +609,8 @@ export const useChatStore = defineStore("chat", () => {
     streamingStatus,
     streamingPendingTool,
     lastContextMeta,
+    ragProjectId,
+    updateRagScope,
     ollamaStatus,
     modelStatus,
     defaultModel,