feat: add server persistence for rosary streak

- Add RosaryStreak MongoDB model for logged-in users
- Add /api/glaube/rosary-streak GET/POST endpoints
- Sync streak to server when logged in, merge local/server data
- Auto-sync when coming back online (PWA offline support)
- Falls back to localStorage for guests

src/routes/api/glaube/rosary-streak/+server.ts

@@ -0,0 +1,61 @@
+import { json, error, type RequestHandler } from '@sveltejs/kit';
+import { RosaryStreak } from '../../../../models/RosaryStreak';
+import { dbConnect } from '../../../../utils/db';
+
+export const GET: RequestHandler = async ({ locals }) => {
+  const session = await locals.auth();
+
+  if (!session?.user?.nickname) {
+    throw error(401, 'Authentication required');
+  }
+
+  await dbConnect();
+
+  try {
+    const streak = await RosaryStreak.findOne({
+      username: session.user.nickname
+    }).lean();
+
+    return json({
+      length: streak?.length ?? 0,
+      lastPrayed: streak?.lastPrayed ?? null
+    });
+  } catch (e) {
+    throw error(500, 'Failed to fetch rosary streak');
+  }
+};
+
+export const POST: RequestHandler = async ({ request, locals }) => {
+  const session = await locals.auth();
+
+  if (!session?.user?.nickname) {
+    throw error(401, 'Authentication required');
+  }
+
+  const { length, lastPrayed } = await request.json();
+
+  if (typeof length !== 'number' || length < 0) {
+    throw error(400, 'Valid streak length required');
+  }
+
+  if (lastPrayed !== null && typeof lastPrayed !== 'string') {
+    throw error(400, 'Invalid lastPrayed format');
+  }
+
+  await dbConnect();
+
+  try {
+    const updated = await RosaryStreak.findOneAndUpdate(
+      { username: session.user.nickname },
+      { length, lastPrayed },
+      { upsert: true, new: true }
+    ).lean();
+
+    return json({
+      length: updated.length,
+      lastPrayed: updated.lastPrayed
+    });
+  } catch (e) {
+    throw error(500, 'Failed to update rosary streak');
+  }
+};