fix(web): reject non-string connected repo branches

[dirtybits]

Summary

• Stack this narrow follow-up on fix(web): reject unsafe connected repo branches #210, which rejects slash/path traversal forms in connected-repository branch names.
• Treat branch as untrusted runtime input in validateRepoCoords: preserve the existing undefined/null default to main, trim strings, and reject numbers, arrays, and objects with the existing Invalid branch result.
• Prevent a validly signed connect-repository request with branch: {} (or another non-string JSON value) from reaching .trim() and returning a server error before repository ownership checks.
• Add direct behavioral regression coverage for representative non-string branch values.

No database schema, repository sync behavior for valid inputs, chain, wallet, payment, or deployment configuration changes.

Verification

• npm test --workspace @agentvouch/web -- __tests__/lib/mirror-connectedRepos.test.ts --maxWorkers=1 --no-fileParallelism — passed (26 tests).
• npm run format:check — passed.
• npm run lint:web — passed.
• npm run typecheck — passed.
• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism — passed (141 files, 1,195 tests).
• git diff --check origin/fix/reject-unsafe-connected-repo-branches...HEAD — passed.
• npm exec --workspace @agentvouch/web -- next build --webpack — webpack compilation and TypeScript passed, but static prerendering stopped at /sitemap.xml because this cron checkout lacks web/.env.local / DATABASE_URL. The pre-existing ox dynamic-dependency warning was also emitted. No full production-build success is claimed.

Rollback

Revert commit 029538b. This restores the prior behavior only; no schema, deployment, or persisted state requires rollback.