feat(crash): privacy-respecting crash reporting via Gitea issue

Capture uncaught exceptions on-device and let the user submit them, by
hand, as a Gitea issue — no network access, no auto-upload (the app holds
no INTERNET permission). Closes prod-readiness item 10; the issue
templates also close item 7.

- CrashReporter: uncaught-exception handler installed first in
  CalendulaApp.onCreate so startup crashes are caught too. Persists an
  allowlist-only report (app/Android/device version, locale, time, stack
  trace — nothing else) to filesDir/crash, then chains to the previous
  handler so the process still dies normally. Crash-loop detection +
  markHealthy reset.
- buildCrashReport is pure/testable; CrashReportBuilderTest asserts the
  header is exactly the allowlisted lines (guards against PII creep).
- Surfacing: next-launch dialog showing the full report verbatim (the
  privacy backstop) with a dismissed-marker so it doesn't nag; a Settings
  "Report a problem" row; and a minimal standalone CrashReportActivity
  that MainActivity routes to on a startup crash-loop, kept clear of the
  Hilt graph / DataStore theme.
- submitCrashReport copies the report to the clipboard and opens the
  prefilled Gitea issues/new URL (long traces fall back to paste).
- .gitea/ISSUE_TEMPLATE: crash_report, bug_report, feature_request.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,16 @@
+---
+name: Feature request
+about: Suggest an idea or improvement
+title: ""
+labels:
+  - enhancement
+---
+
+### What would you like Calendula to do?
+
+
+### Why — what problem does it solve?
+
+
+### Anything else
+<!-- mockups, examples from other apps, alternatives you considered -->