feat: implement SSH honeypot server with auth and config

Add core SSH server with password authentication, per-IP failure
tracking, credential memory with TTL, and static credential support.
Includes TOML config loading with validation, Ed25519 host key
auto-generation, and a Nix package output.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

oubliette.toml.example

@@ -0,0 +1,17 @@
+log_level = "info"
+
+[ssh]
+listen_addr = ":2222"
+host_key_path = "oubliette_host_key"
+
+[auth]
+accept_after = 10
+credential_ttl = "24h"
+
+[[auth.static_credentials]]
+username = "root"
+password = "toor"
+
+[[auth.static_credentials]]
+username = "admin"
+password = "admin"