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/Cargo.toml

@@ -21,6 +21,7 @@ clap = { version = "4", features = ["derive"] }
 crossbeam-channel = "0.5"
 sysinfo = "0.35"
 serde_json = "1"
+rusqlite = { version = "0.32", features = ["bundled"] }
 
 [features]
 default = ["gauntlet"]