feat: initial common-repo source template for semantic releases

Includes:
- .releaserc.yaml (conventionalcommits preset, changelog, git, github, major-tag)
- commitlint.config.js (@commitlint/config-conventional)
- .github/workflows/commitlint.yml (PR commit linting via wagoid/commitlint-github-action)
- .github/workflows/release.yaml (semantic-release on push to main, GitHub App token auth)
- .common-repo.yaml (source-level excludes for README, LICENSE, self-config)

commitlint.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  extends: ["@commitlint/config-conventional"],
+};