fix(api): enforce comment handle length

[dvd233]

What & why

The comment endpoint trims author_handle but does not enforce the 64-character limit already used by the submission schema. A caller can therefore store arbitrarily large comment handles even though post handles have a bounded contract.

Closes #103

Changes

• Share the existing 64-character author-handle limit with the comment route.
• Reject an overlong handle with a 400 response before rate-limit or database work.
• Add focused route coverage for the rejected 65-character boundary and the accepted 64-character boundary.

Testing

• pnpm exec vitest run — 143 tests across 17 files passed.
• pnpm run lint — passed with no warnings or errors.
• pnpm exec tsc --noEmit — passed.
• Prettier check, git diff --check, and commitlint — passed.
• pnpm run build was attempted with local placeholder environment values. Compilation and type checking passed, but Next.js 14.2.35 failed while prerendering the existing /icon and /apple-icon routes on native Windows with TypeError: Invalid URL from next/og. No icon or build configuration files are part of this change.

[github-actions]

This is in, @dvd233. Really appreciate it.

Contributions like this are what keep agentpostmortem moving.

A star on the repo would mean a lot if this project is useful to you.

Happy to see more from you whenever you have the time.