build: drop docker-bake in favor of plain npm (#551)

* build: drop docker-bake in favor of plain npm

Every TypeScript action maintained by actions/* (checkout, setup-node,
setup-go, cache, upload-artifact) uses plain npm scripts. The bake
setup is a docker/* org convention and adds friction for TS work:
contributors need Docker, the dev loop is ~10x slower than npm, and
Alpine-vs-host byte drift in dist/index.js makes PRs bounce.

Replace with the standard pattern:
- .node-version pins Node 24 so contributors and CI agree
- npm scripts (build, lint, format, test, pre-checkin) replace bake
  targets one-for-one
- validate.yml runs lint + a check-dist diff (mirrors actions/setup-node)
  and a vendor check that npm install --package-lock-only is a no-op
- test.yml uses setup-node + sigstore/cosign-installer, drops bake-action
- dependabot-build.yml regenerates dist via npm instead of bake

CONTRIBUTING.md and README development section updated to match.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* build: align scripts and workflows with actions/* convention

Match the standard layout used by actions/checkout, actions/setup-node,
etc.:

- package.json scripts: split format/format-check (Prettier) from
  lint/lint:fix (ESLint), and have pre-checkin run all four (format,
  lint:fix, build, test) in that order.
- validate.yml lint job runs format-check + lint as separate steps.
- test.yml drops the redundant --coverage flag (now in the test script).
- Drop dependabot-build.yml: actions/* don't auto-rebuild dist on
  dependabot PRs; the check-dist style validate / build job catches
  drift and a maintainer rebuilds locally if needed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

package.json

@@ -5,14 +5,12 @@
   "type": "module",
   "scripts": {
     "build": "ncc build src/main.ts --minify --license licenses.txt",
-    "lint": "npm run prettier && npm run eslint",
-    "format": "npm run prettier:fix && npm run eslint:fix",
-    "eslint": "eslint --max-warnings=0 .",
-    "eslint:fix": "eslint --fix .",
-    "prettier": "prettier --check \"./**/*.ts\"",
-    "prettier:fix": "prettier --write \"./**/*.ts\"",
-    "test": "NODE_OPTIONS='--experimental-vm-modules' jest",
-    "all": "npm run build && npm run format && npm test"
+    "format": "prettier --write \"**/*.ts\"",
+    "format-check": "prettier --check \"**/*.ts\"",
+    "lint": "eslint --max-warnings=0 \"**/*.ts\"",
+    "lint:fix": "eslint --fix \"**/*.ts\"",
+    "test": "NODE_OPTIONS='--experimental-vm-modules' jest --coverage",
+    "pre-checkin": "npm run format && npm run lint:fix && npm run build && npm test"
   },
   "repository": {
     "type": "git",