Server: fix idle CPU busy-loop and network-reachable memory-safety bugs

[Leproide]

Performance:

• Main loop used usleep(1) with a non-blocking enet_host_service(..., 0), so it spun millions of times per second and burned about 20% of a core while idle with no clients. Raise the sleep to usleep(1000) (1 ms). A 1 ms tick is far finer than the 30/60 fps network rate; measured idle CPU dropped from about 22% to about 2%.

Network-reachable memory safety (unauthenticated peer, single UDP packet):

• CG_JOINROOM accepted room == 16, indexing roomInfos[16] one past the 16-entry array and writing through it. Reject room >= 16.
• ProcessReceiveEvent cast packet->data to message structs without checking packet->dataLength, allowing out-of-bounds reads from truncated packets (reachable pre-join for CG_JOINROOM). Validate the minimum length per type.

Hardening:

• Player name is now NUL terminated server-side and printed with a bounded %.*s, preventing an over-read of client-controlled bytes.
• Use fprintf(stderr, ...) instead of printf(stderr, ...).
• Print build date/time and strftime output through explicit "%s" formats.
• Check malloc return values in AddPeerLPL and AddIPBanL.

No wire-format or gameplay changes.