fix: ensure system info is loaded before MainShell builds

[SERDUN]

Problem

After an FGS failure (e.g. Xiaomi "did not start in time"), the app could crash with:

StateError: No system info in cache, ensure getLocalSystemInfo() has been called
on logged-in routes after the initial system info load

#0  SystemInfoRepositoryImpl.getLocalSystemInfo  (system_info_repository.dart:96)
#1  _MainShellState.build.<anonymous closure>    (main_shell.dart:257)
...
#6  _MainShellState._pollingRegistrations        (main_shell.dart)

Root cause: CallerIdSettingsRepository.create (and one other provider at line 176) call getLocalSystemInfo() synchronously. The MainShellRoute guard only checked for a valid session token — it did not verify that system info was actually in the cache.

After FGS failure the app can reach MainShellRoute in authenticated state (session token still in SecureStorage) while system info is absent — either because userSessionCleanupResolver.clear() ran in a previous process, or because the initial info fetch was interrupted before setSystemInfo() completed.

Fix

Add getSystemInfo(cacheFirst) to onMainShellRouteGuardNavigation, executed after the auth check:

• If cache already has data → returns immediately (no network call)
• If cache is empty → fetches from network and populates cache before navigation resolves
• If both cache and network fail → redirects to login

SystemInfoRepository is injected into AppRouter via constructor.

Test plan

• Normal launch: MainShell opens, no extra network round-trip (cache hit)
• Clear app data → launch → login → MainShell opens correctly after info fetch
• Simulate no-cache + offline → app redirects to login instead of crashing
• FGS crash on Xiaomi → app recovers to login, not crash