fix(backfill): map Plex username to Tautulli user ID before fetching history

Tautulli get_history requires internal user_id, not Plex ID.
Now queries get_users first, matches by username/email/friendly_name,
then uses matched user's ID for history fetch.

backend/src/routes/auth.ts

@@ -266,6 +266,34 @@ async function backfillUserHistory(user: {
 			);
 		}
 
+		// Map Plex username to Tautulli user ID
+		const usersResponse = await axios.get(`${TAUTULLI_URL}/api/v2`, {
+			params: {
+				apikey: TAUTULLI_API_KEY,
+				cmd: "get_users",
+			},
+		});
+
+		const tautulliUsers = usersResponse.data?.response?.data || [];
+		const tautulliUser = tautulliUsers.find(
+			(u: any) =>
+				u.username?.toLowerCase() === user.plexUsername.toLowerCase() ||
+				u.email?.toLowerCase() === user.plexUsername.toLowerCase() ||
+				u.friendly_name?.toLowerCase() === user.plexUsername.toLowerCase(),
+		);
+
+		if (!tautulliUser) {
+			console.log(
+				`Tautulli user not found for Plex username ${user.plexUsername}, skipping backfill`,
+			);
+			return;
+		}
+
+		const tautulliUserId = tautulliUser.user_id;
+		console.log(
+			`Mapped ${user.plexUsername} to Tautulli user ID ${tautulliUserId}`,
+		);
+
 		// Calculate 30 days ago
 		const thirtyDaysAgo = new Date();
 		thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);
@@ -276,7 +304,7 @@ async function backfillUserHistory(user: {
 			params: {
 				apikey: TAUTULLI_API_KEY,
 				cmd: "get_history",
-				user_id: user.plexId,
+				user_id: tautulliUserId,
 				start_date: startDate,
 				length: 1000,
 			},