Summary

Implements per-user login tracking with a configurable date-range filter on the All Users dashboard. Existing lastLogin field only stored the most recent login (overwritten on each signin); this adds a loginEvents collection capturing one document per signin so administrators can see usage frequency.

Closes CHALK-110, CHALK-111, CHALK-112, CHALK-113, CHALK-114.

Changes

Backend (Firebase.tsx)

• firebaseEmailSignIn writes a doc to a new loginEvents collection on every successful login ({ userId, timestamp }). The existing lastLogin field update is preserved for backward compatibility.
• New method getUsersLoginCounts(start, end): single batch query against loginEvents filtered by timestamp, builds Map<userId, count> in memory. Same optimized pattern as getUsersLastAction().

UI (AllUsersTable.tsx, AllUsersPage.tsx)

• Date range picker (@material-ui/pickers, already in deps) with quick presets: Last 7d / 30d / 90d.
• New Logins column with numeric sort, alongside the existing Last Login column (different info — both useful).
• Default range: last 30 days.
• CSV export includes the login count with a date-stamped header (e.g. Logins (Apr 8 – May 8)).

State management

• AllUsersPage loads users and counts in parallel (Promise.all) on mount.
• Range changes refetch only getUsersLoginCounts (users are not re-queried).

Architectural notes

• Mirrors CHALK-090 (Last Action) pattern — proven, in production since January.
• No Firestore rules update needed — existing rules permit authenticated users to write.
• No Cloud Functions added → no IAM permission constraints.
• Cost: ~600 users × ~2 logins/day ≈ 1.2k writes/day. Well within free tier.

⚠️ Historical data limitation

Login counts begin from the deploy date forward. Past logins were never captured as discrete events — only the most recent was stored (and overwritten). This will be communicated to the client on delivery.

Test plan

• Local Firebase emulator: sign in multiple times, verify docs created in loginEvents
• All Users page: verify Logins column shows correct count for current admin
• Change date range / use presets: counts update without re-loading users list
• Sort by Logins column ascending and descending
• CSV export: header includes formatted date range, count column populated
• Staging deploy: smoke test with seeded data
• Production deploy + verification