docs: add JSDoc to exported functions in server/lib/

[corvid-agent]

Summary

• Added comprehensive JSDoc with @param and @returns tags to all exported functions in 4 server/lib/ files:
  • errors.ts — all error class constructors + isAppError type guard
  • response.ts — json, badRequest, notFound, unavailable, serverError, errorMessage, safeNumParam, handleRouteError
  • secure-wipe.ts — wipeBuffer, wipeBuffers, withSecureBuffer
  • resilience.ts — withRetry, CircuitBreaker class + methods, CircuitOpenError
• No functional changes — documentation only

Closes #1087

Test plan

• bun x tsc --noEmit --skipLibCheck passes
• 101 tests pass across the 4 affected test files (0 failures)
• bun run spec:check — 151/151 passed, 442/442 file coverage

🤖 Generated with Claude Code

[github-actions]

All CI checks passed (tsc, tests) on ubuntu. Cross-platform tests (macOS, Windows) run on release tags only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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