ci+quality: structural gates (CI: 3 new; local: 7 new + .clang-tidy)

CI gates (active on every PR via .gitea/workflows/)
───────────────────────────────────────────────────
1. test-count consistency
   cpp-tests.yml gains a step after test-cgal that runs
   `scripts/check-test-counts.sh` against the just-built ./build dir
   (reuse via new BUILD_DIR env var, ~5 s overhead).  Drift between
   `doc/api/tests.md` and ctest reality now fails the PR.

2. End-to-end smoke
   `scripts/try_it.sh` (the documented user quick-start) is now part of
   the CGAL job, so README quick-start regressions fail the PR rather
   than silently breaking when users land.

3. Internal markdown link checker
   New `.gitea/workflows/markdown-links.yml` + `scripts/check-markdown
   -links.py`.  PRs that touch any *.md file run the check; main pushes
   trigger it too; a weekly cron catches external link rot.  Pure
   Python, no third-party action.  Validated against the current tree:
   122 internal links across 37 *.md files, 0 broken.

Local quality scripts (`scripts/quality/`, not in CI)
─────────────────────────────────────────────────────
* `license-headers.sh`   — `SPDX-License-Identifier: MIT` audit over
                            code/{include,src,tests}/.  Currently
                            reports 60/66 files missing it — that's
                            a follow-up; the script captures the
                            structural gap.
* `sanitizers.sh`        — ASan + UBSan over the fast test suite.
* `coverage.sh`          — gcov/lcov line + branch coverage of
                            code/include/, HTML report under
                            build-coverage/lcov-html/.
* `clang-tidy.sh`        — runs the curated `.clang-tidy` policy over
                            every public header.
* `multi-compiler.sh`    — sequential build + test against every
                            detected g++/clang++ (auto-discovery or
                            explicit list).
* `cgal-version-matrix.sh`— sequential build + CGAL test suite against
                            every CGAL tree under `~/cgal/<ver>/` (or
                            via `CGAL_ROOTS=...` env var).
* `reproducible-build.sh`— two `Release -j1` builds, fail if any test
                            executable byte-differs.
* `run-all.sh`           — driver: `--fast` for the ~5-min subset,
                            no arg for the ~25–40 min full sweep;
                            captures per-gate logs to
                            build-quality-logs/.

+ `.clang-tidy`          — curated, deliberately-small policy (only
                            checks that fire on OUR code, never on
                            transitive CGAL/Eigen/Boost headers).

+ `scripts/quality/README.md` — explains the structure, lists each
                            gate's wall-time + prereqs, and codifies
                            the promotion path: a gate moves into CI
                            only when it's green on the dev machine
                            AND has a recovery-instructions paragraph
                            in `doc/release-policy.md`.

Doc updates
───────────
`doc/architecture/locked-vs-flexible.md` (reviewer-facing) gains 4
"closed" rows in the limitations table — the 3 CI gates above and the
local quality-script suite.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/cpp-tests.yml

@@ -96,3 +96,19 @@ jobs:
             passed=$(( ${total:-0} - ${failed:-0} - ${skipped:-0} ))
             echo "CGAL  ▸ TOTAL ${total:-0} | PASSED $passed | FAILED ${failed:-0} | SKIPPED ${skipped:-0}"
           fi
+
+      # ── Structural gate: doc/api/tests.md totals match ctest reality ───
+      # Single source of truth for test counts (see doc/release-policy.md).
+      # Reuses the already-built ./build dir via BUILD_DIR env var, so this
+      # adds ~5 s on top of the existing CGAL job.
+      - name: Verify test-count consistency (doc/api/tests.md)
+        run: BUILD_DIR=build bash scripts/check-test-counts.sh
+
+      # ── Structural gate: end-to-end smoke (try_it.sh) ──────────────────
+      # The user-facing quick-start script: configure + build + run the
+      # full ctest + run the Euclidean example on a bundled mesh.  If
+      # this regresses, README quick-start instructions are broken.
+      # try_it.sh creates its own build-try/ — accept the ~3 min cost as
+      # the price of guaranteeing the documented workflow stays working.
+      - name: End-to-end smoke test (scripts/try_it.sh)
+        run: bash scripts/try_it.sh