feat: timezone support + granular backup schedule — closes #131

Based on PR #135 by @andreibrebene with adjustments:
- TZ environment variable for Docker timezone support
- Granular auto-backup schedule (hour, day of week, day of month)
- UTC timestamp fix for admin panel
- Server timezone exposed in app-config API
- Replaced native selects with CustomSelect for consistent UI
- Backup schedule UI with 12h/24h time format support

Thanks @andreibrebene for the implementation!

server/src/routes/admin.ts

@@ -12,6 +12,11 @@ const router = express.Router();
 
 router.use(authenticate, adminOnly);
 
+function utcSuffix(ts: string | null | undefined): string | null {
+  if (!ts) return null;
+  return ts.endsWith('Z') ? ts : ts.replace(' ', 'T') + 'Z';
+}
+
 router.get('/users', (req: Request, res: Response) => {
   const users = db.prepare(
     'SELECT id, username, email, role, created_at, updated_at, last_login FROM users ORDER BY created_at DESC'
@@ -21,7 +26,13 @@ router.get('/users', (req: Request, res: Response) => {
     const { getOnlineUserIds } = require('../websocket');
     onlineUserIds = getOnlineUserIds();
   } catch { /* */ }
-  const usersWithStatus = users.map(u => ({ ...u, online: onlineUserIds.has(u.id) }));
+  const usersWithStatus = users.map(u => ({
+    ...u,
+    created_at: utcSuffix(u.created_at),
+    updated_at: utcSuffix(u.updated_at as string),
+    last_login: utcSuffix(u.last_login),
+    online: onlineUserIds.has(u.id),
+  }));
   res.json({ users: usersWithStatus });
 });
 

server/src/routes/auth.ts

@@ -28,6 +28,11 @@ function getPendingMfaSecret(userId: number): string | null {
   return row.secret;
 }
 
+function utcSuffix(ts: string | null | undefined): string | null {
+  if (!ts) return null;
+  return ts.endsWith('Z') ? ts : ts.replace(' ', 'T') + 'Z';
+}
+
 function stripUserForClient(user: User): Record<string, unknown> {
   const {
     password_hash: _p,
@@ -39,6 +44,9 @@ function stripUserForClient(user: User): Record<string, unknown> {
   } = user;
   return {
     ...rest,
+    created_at: utcSuffix(rest.created_at),
+    updated_at: utcSuffix(rest.updated_at),
+    last_login: utcSuffix(rest.last_login),
     mfa_enabled: !!(user.mfa_enabled === 1 || user.mfa_enabled === true),
   };
 }
@@ -146,6 +154,7 @@ router.get('/app-config', (_req: Request, res: Response) => {
     demo_mode: isDemo,
     demo_email: isDemo ? 'demo@trek.app' : undefined,
     demo_password: isDemo ? 'demo12345' : undefined,
+    timezone: process.env.TZ || Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC',
   });
 });
 

server/src/routes/backup.ts

@@ -212,17 +212,30 @@ router.post('/upload-restore', uploadTmp.single('backup'), async (req: Request,
 
 router.get('/auto-settings', (_req: Request, res: Response) => {
   try {
-    res.json({ settings: scheduler.loadSettings() });
+    const tz = process.env.TZ || Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC';
+    res.json({ settings: scheduler.loadSettings(), timezone: tz });
   } catch (err: unknown) {
     console.error('[backup] GET auto-settings:', err);
     res.status(500).json({ error: 'Could not load backup settings' });
   }
 });
 
+function parseIntField(raw: unknown, fallback: number): number {
+  if (typeof raw === 'number' && Number.isFinite(raw)) return Math.floor(raw);
+  if (typeof raw === 'string' && raw.trim() !== '') {
+    const n = parseInt(raw, 10);
+    if (Number.isFinite(n)) return n;
+  }
+  return fallback;
+}
+
 function parseAutoBackupBody(body: Record<string, unknown>): {
   enabled: boolean;
   interval: string;
   keep_days: number;
+  hour: number;
+  day_of_week: number;
+  day_of_month: number;
 } {
   const enabled = body.enabled === true || body.enabled === 'true' || body.enabled === 1;
   const rawInterval = body.interval;
@@ -230,17 +243,11 @@ function parseAutoBackupBody(body: Record<string, unknown>): {
     typeof rawInterval === 'string' && scheduler.VALID_INTERVALS.includes(rawInterval)
       ? rawInterval
       : 'daily';
-  const rawKeep = body.keep_days;
-  let keepNum: number;
-  if (typeof rawKeep === 'number' && Number.isFinite(rawKeep)) {
-    keepNum = Math.floor(rawKeep);
-  } else if (typeof rawKeep === 'string' && rawKeep.trim() !== '') {
-    keepNum = parseInt(rawKeep, 10);
-  } else {
-    keepNum = NaN;
-  }
-  const keep_days = Number.isFinite(keepNum) && keepNum >= 0 ? keepNum : 7;
-  return { enabled, interval, keep_days };
+  const keep_days = Math.max(0, parseIntField(body.keep_days, 7));
+  const hour = Math.min(23, Math.max(0, parseIntField(body.hour, 2)));
+  const day_of_week = Math.min(6, Math.max(0, parseIntField(body.day_of_week, 0)));
+  const day_of_month = Math.min(28, Math.max(1, parseIntField(body.day_of_month, 1)));
+  return { enabled, interval, keep_days, hour, day_of_week, day_of_month };
 }
 
 router.put('/auto-settings', (req: Request, res: Response) => {