feat(simulation): SQLite settings storage with IPC protocol v20 (#627)

Per-player settings via rusqlite (bundled, zero runtime dep). Server
owns the settings DB; client sends ChangeSettings commands over IPC.
Extensible key-value with typed columns (String/Int/Float/Bool).
Protocol bumped to v20 with settings_response in ObserverSnapshot.

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

server/tests/bridge_ipc.rs

@@ -77,6 +77,7 @@ fn snapshot_roundtrip_over_unix_socket() {
         debug_response: None,
             sim_errors: vec![],
             current_ticker: None,
+            settings_response: None,
         };
 
         bridge