ntp: use NTP-corrected time everywhere instead of unixepoch()/gettimeofday

- db_sync_next_timestamp(): ntp_time_get_us() via si->db_sync->inst
- topo_node_sqlite_node_put: +time_t now_sec param, replace unixepoch()
- topo_node_sqlite_node_update_verified: +time_t created_at param
- topo_node_sqlite_member_put: joined_at = join_ts (already NTP-corrected)
- All INSERTs (nodes, local_identity, accounts, peers):
  replace DEFAULT(unixepoch()) with explicit ntp_time_get_seconds()
- ON CONFLICT DO UPDATE: created_at = COALESCE(nodes.created_at, excluded.created_at)
- Updated callers: topo_group.c, chat_sync.c, chat_conn_mgr.c, chat_core.c

src/routing_layer/topo_node_sqlite.h

@@ -4,6 +4,7 @@
 #include <sqlite3.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <time.h>
 
 struct TOPO_NODEQ;
 
@@ -16,7 +17,7 @@ struct TOPO_NODEQ;
 
 int topo_node_sqlite_init(sqlite3* db);
 
-int topo_node_sqlite_node_put(sqlite3* db, struct TOPO_NODEQ* nq);
+int topo_node_sqlite_node_put(sqlite3* db, struct TOPO_NODEQ* nq, time_t now_sec);
 
 int topo_node_sqlite_channel_put(sqlite3* db, const char* channel_id,
     const char* name, uint64_t owner_node_id,
@@ -36,7 +37,7 @@ int topo_node_sqlite_member_get_join(sqlite3* db, const char* channel_id, uint64
 int topo_node_sqlite_member_del(sqlite3* db, const char* channel_id, uint64_t node_id);
 
 int topo_node_sqlite_node_update_verified(sqlite3* db, uint64_t node_id,
-    const char* name, const uint8_t* x25519, const uint8_t* ed25519, uint64_t update_ts);
+    const char* name, const uint8_t* x25519, const uint8_t* ed25519, uint64_t update_ts, time_t created_at);
 
 int topo_node_sqlite_channel_get(sqlite3* db, const char* channel_id,
     char* name_out, int name_sz, uint64_t* owner_node_id,