fold redundant test_coverage.sh into the gate

`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>

Makefile

@@ -102,12 +102,8 @@ test-e2e: ## End-to-end Playwright smoke.
 .PHONY: test-all
 test-all: test-core test test-a11y test-integration test-e2e ## Everything, sequentially.
 
-.PHONY: coverage
-coverage: ## flutter test --coverage + lcov summary.
-	ci/test_coverage.sh
-
 .PHONY: coverage-gate
-coverage-gate: ## Coverage gate — fails if total line % < coverage/floor.txt (D-66). Assumes `make test` ran first.
+coverage-gate: ## Coverage gate — fails if total line % < pubspec.yaml `coverage_floor:` (D-66). Assumes `make test` ran first.
 	ci/coverage_gate.sh
 
 .PHONY: smoke-bundle