Add scripts-to-rule-them-all scaffold (closes #4)

Adopt the Scripts to Rule Them All standard for this Hugo site:

- script/ POSIX-sh entrypoints (bootstrap, setup, projectname, test,
  lint, fmt, fmt-check, check, docker, cibuild, precommit,
  install-precommit). The correctness check (test/lint) is a clean
  `hugo --minify` production build; fmt/fmt-check run prettier over the
  repo's own top-level markdown only, leaving content/ untouched.
- Makefile targets reduced to thin shims that call script/NAME, plus a
  convenience serve target for `hugo server`.
- Dockerfile on a sha256-pinned alpine base that installs deps via
  script/bootstrap and runs `make check`, so the image build fails on
  any formatting or Hugo build error; .dockerignore added.
- .gitea/workflows/check.yml runs script/cibuild on push.
- README Entrypoints section documenting the scripts.

.gitea/workflows/check.yml

@@ -0,0 +1,9 @@
+name: check
+on: [push]
+jobs:
+    check:
+        runs-on: ubuntu-latest
+        steps:
+            # actions/checkout v4.2.2, 2026-02-28
+            - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+            - run: script/cibuild