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/src/simulation/input.rs

@@ -4,6 +4,7 @@
 
 use crate::bridge::debug::DebugCommandBuffer;
 use crate::bridge::types::{FacingDirection, ObjectType, PlayerAction, PlayerInput};
+use crate::settings::{SettingsCommand, SettingsCommandBuffer};
 use crate::knowledge::{EntityRegistry, StableId};
 use crate::perception::vision_cone::{facing_from_delta, Facing};
 use crate::simulation::interaction::{DoorInteractRequest, DoorState, TerminalInteractRequest};
@@ -100,6 +101,7 @@ pub fn process_player_input(
     mut room_snapshots: Option<ResMut<RoomSnapshots>>,
     mut save_load: Option<ResMut<SaveLoadPending>>,
     mut debug_cmd_buffer: Option<ResMut<DebugCommandBuffer>>,
+    mut settings_cmd_buffer: Option<ResMut<SettingsCommandBuffer>>,
     door_states: Query<&DoorState>,
     object_types: Query<&ObjectType>,
 ) {
@@ -122,6 +124,9 @@ pub fn process_player_input(
                     | PlayerAction::SaveGame { .. }
                     | PlayerAction::LoadGame { .. }
                     | PlayerAction::DebugCommand(_)
+                    | PlayerAction::ChangeSetting { .. }
+                    | PlayerAction::RequestAllSettings
+                    | PlayerAction::DeleteSetting { .. }
             )
         {
             continue;
@@ -374,6 +379,27 @@ pub fn process_player_input(
                     tracing::warn!("DebugCommand received but DebugCommandBuffer not registered");
                 }
             }
+            PlayerAction::ChangeSetting { key, value } => {
+                if let Some(ref mut buf) = settings_cmd_buffer {
+                    buf.push(SettingsCommand::Change { key, value });
+                } else {
+                    tracing::warn!("ChangeSetting received but SettingsCommandBuffer not registered");
+                }
+            }
+            PlayerAction::RequestAllSettings => {
+                if let Some(ref mut buf) = settings_cmd_buffer {
+                    buf.push(SettingsCommand::RequestAll);
+                } else {
+                    tracing::warn!("RequestAllSettings received but SettingsCommandBuffer not registered");
+                }
+            }
+            PlayerAction::DeleteSetting { key } => {
+                if let Some(ref mut buf) = settings_cmd_buffer {
+                    buf.push(SettingsCommand::Delete { key });
+                } else {
+                    tracing::warn!("DeleteSetting received but SettingsCommandBuffer not registered");
+                }
+            }
         }
     }