Add scripts-to-rule-them-all scaffold (refs #1)

Add the standard STRTA scaffold, mirroring the conformant Go repos:

- script/ POSIX-sh entrypoints (bootstrap, setup, projectname, test,
  lint, fmt, fmt-check, check, docker, cibuild, precommit,
  install-precommit).
- Makefile rewritten as thin shims: .PHONY plus the nine standard
  targets each delegating to script/NAME; repo-specific build, clean,
  and try targets retained.
- .golangci.yml matching the org-standard Go lint config.
- Dockerfile whose build runs make check then make build, so the image
  fails on any check failure.
- .gitea/workflows/check.yml running script/cibuild.

make fmt-check and make test are green. make check is not yet green
because of pre-existing lint findings in the application code, which
are out of scope for this scaffold change; hence refs (not closes).

script/precommit

@@ -0,0 +1,21 @@
+#!/bin/sh
+# script/precommit: run by the git pre-commit hook; fails the commit if
+# checks fail. Our own extension to scripts-to-rule-them-all. Go extra:
+# go mod tidy must be a no-op before the checks run.
+set -eu
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    go mod tidy
+    if ! git diff --exit-code -- go.mod go.sum; then
+        echo "precommit: go mod tidy changed go.mod/go.sum;" \
+            "stage the changes and retry" >&2
+        exit 1
+    fi
+    "$SCRIPT_DIR/check"
+}
+
+main "$@"