Refresh both AGENTS guides and clarify module purpose, usage, ownership, threading, return values and wire formats in headers. Remove the unused timeout_heap freed_count field and unimplemented getter.
- etcp_router.h/c: new flag ROUTER_FLAG_ENCRYPTED (0x04), etcp_route_send_encrypted(), inflight/retrans/send_q support - utun_instance.h: e2e_ctx_cache[8] — per-peer sc_context_t cache with derived session key - topo_node.c: topo_node_sign_self() — single point for Ed25519 self-signing of NODEINFO - topo_node.c: fix stale x25519_self_sig after address update (topo_node_sign_self call) - nat_detection.c: fix stale x25519_self_sig after in-place socket meta modification - test_etcp_router_unit: 5 E2E tests (basic round-trip, no NODEINFO drop, tampered, cache reuse, ENCRYPTED+SIGNED combined) - builds clean, 70/70 tests pass
evgeny