`ci/test.sh` now runs `flutter test --coverage`, so
`ci/test_coverage.sh` was just re-running the same tests plus an
optional `lcov --summary` that needs `lcov` installed (it wasn't,
on at least this machine). Removing it.
- ci/test_coverage.sh: deleted.
- Makefile: drop the `coverage` target (it only wrapped the dead
script). Fix a stale `coverage/floor.txt` reference in the
`coverage-gate` help text — the floor lives in pubspec.yaml now.
- .gitea/workflows/test.yml: replace the test_coverage.sh invocation
with ci/coverage_gate.sh, so CI enforces the same floor as the
pre-push hook (defense in depth).
Co-Authored-By: Claude <noreply@anthropic.com>