- Implement validate_peer_count() in startup_validation.c: -EINVAL for even N>1
- Implement validate_cert_files() with err_buf output: access() check, writes
missing path into err_buf, returns -ENOENT
- Wire validate_peer_count() in main.c after peer list parse; fatal exit on fail
- Wire validate_cert_files() in main.c before SSL init; fatal exit on fail
- Fix ASAN leak: SSL_CTX_free in ha_fini() with NULL guard
- Fix double-free: null c->ha.ssl_ctx in cluster_fini() before ha_fini(),
so iomgr_fini() retains sole SSL_CTX ownership (design per ha.h comment)
- All 96 tests pass; all 12 ha_startup tests GREEN