feat(errors): install global error hooks in main()

## Problem
(verified) `lib/main.dart:151-166` — `main()` initializes CAMS and the bloc with no error handling; an exception in `bloc.initialize()` (e.g., backend down) prevents `runApp` entirely with no user-facing state.

## Proposed fix
Add `FlutterError.onError` and `PlatformDispatcher.instance.onError` handlers (log + report); wrap startup so initialization failure still renders an error/retry screen instead of a dead app.

## Acceptance criteria
- [ ] Sync widget error, async error, and startup-init failure each produce a report
- [ ] Startup failure shows a visible retry UI

**Effort:** S · **Priority:** P1 · **Change risk:** Low