♻️ Adopt setup: prefix and retire the stray use: script

Introduce a setup: prefix for one-time clone configuration (mutates the
local environment, never a hook or CI step) with setup as its umbrella
aggregator. Move use:git-commit-message to setup:git-commit-message as
its first member, retiring use: — the undocumented prefix tracked in the
backlog. Update both CONTRIBUTING.md prefix lists, the bare-command
inventory, and the stale use: reference in branch.sh.

package.json

@@ -62,7 +62,8 @@
         "watch:test": "node --test --watch --strip-types \"src/**/*.test.ts\"",
         "publish:attw": "attw . --pack --profile esm-only",
         "publish:publint": "publint",
-        "use:git-commit-message": "git config commit.template commit-message-template"
+        "setup": "npm run setup:git-commit-message",
+        "setup:git-commit-message": "git config commit.template commit-message-template"
     },
     "devDependencies": {
         "@arethetypeswrong/cli": "^0.18.5",