Repo overview logs README 404 for repos without a README

[shuv1337]

Problem / Context

Loading an uncached repo overview logs a server-side 404 when fetching the README:

GET /repos/shuv1337/oak-spike/readme?ref=main - 404

The page still renders, but the console shows an error on first cold visit. Repos without a README (or with README on a non-default branch) should not produce error-level console noise.

Source: dogfood-output/cache-dogfood-report.md (ISSUE-004)

Reproduction

1. Authenticate locally
2. Open an uncached repo without a README on main, e.g. http://127.0.0.1:3000/shuv1337/oak-spike
3. Check server/console logs during first load

Acceptance Criteria

• Repos without a README show an intentional empty state — no 404 logged as an error
• README fetch treats 404 as expected/absent, not a failure path
• Overview still renders correctly for README-less repos
• Cache warming/population handles absent README gracefully

Evidence

• dogfood-output/benchmarks/console-cold-overview-oak-spike-run-1.txt (readme 404 at line ~98)
• dogfood-output/screenshots/cache-cold-overview-oak-spike-run-1.png

Implementation Notes

Likely the overview route or README loader treats GitHub's 404 as an exceptional case and logs at error level. Handle 404 as readme: null and render the existing empty README UI without server error logging.

Tasks

• Find README fetch path for repo overview
• Downgrade/handle 404 as expected absence
• Add or verify empty-state UI for no README
• Confirm clean console on cold visit to shuv1337/oak-spike