#21727: skills: treat allowBundled [] as denylist for bundled skills

## Summary - Fixes an issue where `skills.allowBundled: []` was being normalized to `undefined` and interpreted as an allow-all state. - Normalizes allowlist values to preserve empty arrays so empty config is now treated as an explicit denylist. - Updates bundled-skill eligibility logic so: - `allowBundled: undefined` keeps current behavior (bundled skills allowed by default). - `allowBundled: []` blocks all bundled skills. - Adds e2e regression coverage in `src/agents/skills.buildworkspaceskillstatus.e2e.test.ts`. ## Testing - `pnpm vitest run --config vitest.e2e.config.ts src/agents/skills.buildworkspaceskillstatus.e2e.test.ts` - `pnpm test:fast` Closes #21709. <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes a normalization bug where `allowBundled: []` was incorrectly treated as allow-all instead of deny-all. The change preserves empty arrays through normalization and adds explicit logic to distinguish between undefined (default allow-all) and empty array (explicit deny-all). E2e test coverage added for the empty array case. <h3>Confidence Score: 5/5</h3> - Safe to merge - clean bug fix with targeted changes and test coverage - The fix is minimal and focused, changing only the normalization logic to preserve empty arrays. The distinction between `undefined` (allow-all) and `[]` (deny-all) is now explicit and well-tested. No breaking changes to existing functionality. - No files require special attention _{Last reviewed commit: 344cda1} <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->