p2p(kademlia): Unbounded address accumulation from Identify Push messages

[euxaristia]

Summary

Every Identify event copies advertised listen addresses into Kademlia without a per-peer maximum, TTL, or replacement policy (crates/gitlawb-node/src/p2p/mod.rs:365-371).

Impact

A peer advertising fresh valid multiaddrs over repeated Identify Push messages continuously inflates retained address state.

Remediation

1. Enforce a small per-peer address maximum with eviction.
2. Apply TTL to addresses.
3. Rate-limit Identify Push processing.

Fix

Addressed in #410.