fix(flutter): tighten version-check cadence to 1m during active use

Drops the staleness gate from 1h to 1m and adds a Timer.periodic that
fires recheckIfStale every minute while the app is foregrounded. Net
effect: ~1 check per minute of active use, ~60 KB/hr data — trivially
affordable for the value of faster recovery when min_client_version
bumps server-side.

Timer is paired with the lifecycle observer: started in initState +
on resume, stopped in dispose + on pause/inactive/hidden/detached so
backgrounded apps don't burn battery on probes the user can't see.

Staleness gate still wraps the call so concurrent triggers (timer +
resume firing close together) dedupe to one network call. Manual
"Check now" still bypasses the gate via recheck().

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/shared/widgets/version_gate.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:dio/dio.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
@@ -50,7 +52,12 @@ String _stringFromResult(VersionResult r) {
 class VersionCheckController extends AsyncNotifier<VersionResult> {
   static const _kResult = 'version_check_result';
   static const _kAtMs = 'version_check_at_ms';
-  static const _staleMs = 60 * 60 * 1000; // 1h
+  // 1 minute. The /healthz response is sub-1KB and the call is
+  // non-blocking, so a tight cadence buys faster recovery from
+  // server-side min_client_version bumps without measurable cost. The
+  // gate also acts as a safety net against duplicate calls when the
+  // periodic timer and a resume event fire close together.
+  static const _staleMs = 60 * 1000;
 
   @override
   Future<VersionResult> build() async {
@@ -151,6 +158,13 @@ class VersionGate extends ConsumerStatefulWidget {
 
 class _VersionGateState extends ConsumerState<VersionGate>
     with WidgetsBindingObserver {
+  // Polling interval during active foreground use. Paired with the
+  // controller's 1m staleness gate so concurrent fires (timer + resume)
+  // dedupe to a single network call. Tight cadence is affordable —
+  // /healthz is sub-1KB and the call is non-blocking.
+  static const _pollInterval = Duration(minutes: 1);
+  Timer? _pollTimer;
+
   @override
   void initState() {
     super.initState();
@@ -158,20 +172,46 @@ class _VersionGateState extends ConsumerState<VersionGate>
     // hydrates from cache + fires a background check when stale.
     ref.read(versionCheckProvider);
     WidgetsBinding.instance.addObserver(this);
+    _startPolling();
   }
 
   @override
   void dispose() {
+    _stopPolling();
     WidgetsBinding.instance.removeObserver(this);
     super.dispose();
   }
 
-  @override
-  void didChangeAppLifecycleState(AppLifecycleState state) {
-    if (state == AppLifecycleState.resumed) {
-      // Staleness-gated: cheap when the user just briefly left the app.
+  void _startPolling() {
+    _pollTimer?.cancel();
+    _pollTimer = Timer.periodic(_pollInterval, (_) {
       // ignore: unawaited_futures
       ref.read(versionCheckProvider.notifier).recheckIfStale();
+    });
+  }
+
+  void _stopPolling() {
+    _pollTimer?.cancel();
+    _pollTimer = null;
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    switch (state) {
+      case AppLifecycleState.resumed:
+        // Re-arm the timer + fire one immediate (staleness-gated) check
+        // so users who foreground after a long away period get a fresh
+        // result without waiting for the next tick.
+        // ignore: unawaited_futures
+        ref.read(versionCheckProvider.notifier).recheckIfStale();
+        _startPolling();
+      case AppLifecycleState.paused:
+      case AppLifecycleState.inactive:
+      case AppLifecycleState.hidden:
+      case AppLifecycleState.detached:
+        // Stop firing while backgrounded — no need to burn battery on
+        // health probes the user can't see the result of.
+        _stopPolling();
     }
   }