Phase 6: Activity log and notifications

Add activity logging to all write API routes, notification system with
real-time delivery via Socket.IO, @mention parsing in comments, activity
feed sidebar on board page, per-card activity in card modal, and
notification bell with unread badge in the navbar.

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

src/routes/api/boards/[boardId]/+server.ts

@@ -4,6 +4,7 @@ import { boardSchema } from '$lib/server/validation.js';
 import { withTenant } from '$lib/server/rls.js';
 import { requireBoardView, requireBoardEditor, requireBoardOwner } from '$lib/server/guards.js';
 import { broadcast } from '$lib/server/realtime.js';
+import { logActivity } from '$lib/server/activity.js';
 
 // Get single board with all columns and cards
 export const GET: RequestHandler = async ({ params, locals }) => {
@@ -31,14 +32,24 @@ export const PATCH: RequestHandler = async ({ params, request, locals }) => {
 	const updated = await withTenant(tenant.id, async (tx) => {
 		await requireBoardEditor(tx, locals.user, params.boardId, tenant.id);
 
-		return tx.board.update({
+		const board = await tx.board.update({
 			where: { id: params.boardId },
 			data: result.data
 		});
+
+		await logActivity(tx, {
+			boardId: params.boardId,
+			userId: locals.user!.id,
+			action: 'board.updated',
+			metadata: result.data
+		});
+
+		return board;
 	});
 
 	const socketId = request.headers.get('X-Socket-ID');
 	broadcast(params.boardId, 'board:updated', { board: updated, socketId });
+	broadcast(params.boardId, 'activity:new', { boardId: params.boardId, socketId });
 
 	return json({ board: updated });
 };
@@ -50,6 +61,13 @@ export const DELETE: RequestHandler = async ({ params, request, locals }) => {
 
 	await withTenant(tenant.id, async (tx) => {
 		await requireBoardOwner(tx, locals.user, params.boardId, tenant.id);
+
+		await logActivity(tx, {
+			boardId: params.boardId,
+			userId: locals.user!.id,
+			action: 'board.deleted'
+		});
+
 		await tx.board.delete({ where: { id: params.boardId } });
 	});