Add Opera cache cleaner extension baseline

opera-cache-cleaner-extension/docs/release-checklist.md

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+# Release Checklist
+
+## Version
+
+- [ ] Version number updated in `manifest.json`.
+- [ ] `CHANGELOG.md` updated.
+- [ ] README checked for current installation and usage instructions.
+
+## Quality
+
+- [ ] Working tree is clean.
+- [ ] `node --check background.js` passes.
+- [ ] `node --check popup/popup.js` passes.
+- [ ] Manual unpacked-extension smoke test in Opera passes.
+
+## Security
+
+- [ ] `docs/security-review.md` is current.
+- [ ] No new permissions were added without review.
+- [ ] No secrets are committed.
+- [ ] Release artifact does not contain local config files.
+
+## Artifacts
+
+- [ ] `dist/opera-cache-cleaner-extension.zip` exists.
+- [ ] Zip contains `manifest.json`, `background.js`, `popup/`, and `icons/`.
+- [ ] Zip does not contain `dist/`, `.git/`, `.codex/`, `.gitea/`, or docs-only files.
+
+## Release
+
+- [ ] Git tag created.
+- [ ] Release notes written.
+- [ ] Release published.
+- [ ] Post-release download smoke test completed.