fix(api): validate connected repo route pubkeys

[dirtybits]

Summary

• reject malformed public Solana pubkeys on GET /api/agents/[pubkey]/repos before database initialization
• align the public connected-repos route with sibling agent identity and trust route validation
• add a regression proving malformed keys do not invoke database or repository lookups

Test Plan

• npm test --workspace @agentvouch/web -- __tests__/api/connected-repos-skip-review.test.ts --maxWorkers=1 --no-fileParallelism
• npm run format:check
• npm run lint:web
• npm run typecheck
• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism
• npm exec --workspace @agentvouch/web -- next build --webpack
• git diff --check

Notes

No live database, GitHub ownership verification, wallet, or deployment flow was run. The webpack build passed with the repository's existing ox dynamic-dependency warning and expected static-generation fallback logs because local DATABASE_URL is absent.