feat: add persistence/HA system constants to config.h with tests (P0-A)

Adds 17 compile-time constants covering WAL format, HA topology,
snapshot sizing, and operational defaults. test_persistence_constants
in test_config.c validates every constant value; all 6 config tests
pass (4 pre-existing unrelated failures unchanged).

src/include/config.h

@@ -71,4 +71,26 @@ typedef uint64_t jobid_t;
 #define REGEX_JOBARRAY_ID                                                      \
     "[ \t]*([0-9]+)-([0-9]+)-([0-9]+)-([0-9]+)\\[([0-9]+)\\][ \t]*"
 
+/* ======================================================
+ * Persistence & HA system constants (Part 2.6, Appendix A.10)
+ * ====================================================== */
+#define MAX_STANDBYS                    3
+#define MAX_HA_CANDIDATES               4
+#define WAL_FORMAT_VERSION              1
+#define WAL_ENTRY_TYPE_MAX              100    /* WAL_CHECKPOINT = 100, highest known type */
+#define MAX_WAL_PAYLOAD_BYTES           (1 << 20)           /* 1 MB per replication entry */
+#define MAX_SNAPSHOT_BYTES              (256 * 1024 * 1024) /* 256 MB max snapshot size */
+#define WAL_HDR_CRC_SIZE                32     /* sizeof(wal_entry_hdr_t) - 2*sizeof(uint32_t) */
+#define WAL_CRC_NONE                    0xFFFFFFFFu  /* sentinel: no predecessor in chain */
+
+#define DEFAULT_WAL_SYNC_MS             10
+#define DEFAULT_SNAP_INTERVAL_S         60
+#define DEFAULT_SNAP_WAL_SIZE_MB        64
+#define DEFAULT_SNAP_KEEP_N             2
+#define DEFAULT_TRANSIENT_JOB_TIMEOUT_S 300
+#define DEFAULT_FINISHED_RETAIN_S       3600
+#define DEFAULT_WORKER_RETAIN_S         86400
+#define DEFAULT_SYNC_TIMEOUT_MS         50
+#define DEFAULT_HB_INTERVAL_MS          3000
+
 #endif