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>

src/fabledassistant/routes/chat.py

@@ -187,6 +187,28 @@ async def generation_stream_route(conv_id: int):
     )
 
 
+@chat_bp.route("/conversations/<int:conv_id>/generation/confirm", methods=["POST"])
+@login_required
+async def confirm_generation_route(conv_id: int):
+    """Resolve a pending tool confirmation (accept or decline)."""
+    uid = get_current_user_id()
+    conv = await get_conversation(uid, conv_id)
+    if conv is None:
+        return jsonify({"error": "Conversation not found"}), 404
+
+    buf = get_buffer(conv_id)
+    if buf is None or buf.state != GenerationState.RUNNING:
+        return jsonify({"error": "No active generation"}), 404
+
+    if buf.confirmation_future is None or buf.confirmation_future.done():
+        return jsonify({"error": "No pending tool confirmation"}), 409
+
+    data = await request.get_json(force=True, silent=True) or {}
+    decision = bool(data.get("confirmed", False))
+    buf.confirmation_future.set_result(decision)
+    return jsonify({"status": "ok", "confirmed": decision})
+
+
 @chat_bp.route("/conversations/<int:conv_id>/generation/cancel", methods=["POST"])
 @login_required
 async def cancel_generation_route(conv_id: int):