Add tool confirmation UI with Accept/Decline for write operations

Before executing any write tool (create/update/delete), the backend now
pauses with an asyncio.Future and emits a tool_pending SSE event. The
frontend displays a ToolConfirmCard with Accept and Decline buttons.
Clicking Accept resolves the Future and proceeds; Decline records a
declined tool_call chip and falls through to regular streaming. Typing
single-word yes/no responses (e.g. "yes", "cancel") also works as
confirmation. 120s timeout auto-declines if no response.

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

frontend/src/views/ChatView.vue

@@ -7,6 +7,7 @@ import { apiGet } from "@/api/client";
 import { renderMarkdown } from "@/utils/markdown";
 import ChatMessage from "@/components/ChatMessage.vue";
 import ToolCallCard from "@/components/ToolCallCard.vue";
+import ToolConfirmCard from "@/components/ToolConfirmCard.vue";
 import type { Note } from "@/types/note";
 
 const route = useRoute();
@@ -402,6 +403,12 @@ onUnmounted(() => {
                     :tool-call="tc"
                   />
                 </div>
+                <ToolConfirmCard
+                  v-if="store.streamingPendingTool"
+                  :pending-tool="store.streamingPendingTool"
+                  @accept="store.confirmTool(true)"
+                  @decline="store.confirmTool(false)"
+                />
                 <div v-if="store.streamingStatus" class="streaming-status-line">
                   <span class="streaming-status-dot"></span>
                   {{ store.streamingStatus }}