fix(simulation): use non-blocking TCP to prevent game loop stall

read_framed() called read_exact() which blocked the entire bevy Update
schedule waiting for client input — no systems ran until a keystroke
arrived. Switch TcpStream to non-blocking mode so receive_inputs()
returns Ok(vec![]) on WouldBlock instead of blocking. Toggle to
blocking for snapshot writes (reliable delivery). Add 50ms frame
throttle (~20 ticks/sec) since the non-blocking loop would otherwise
spin. Downgrade input receive logging to trace, add error logging for
missing bridge resource and failed observer queries.

Fixes bug #1 (server never sends snapshots) and #2 (camera doesn't
center until first keystroke).

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

server/src/perception/observer/mod.rs

@@ -33,6 +33,7 @@ pub fn compute_visibility_geometry(
     mut geometry: ResMut<VisibilityGeometry>,
 ) {
     let Ok((observer_pos, facing_opt)) = observer_query.single() else {
+        tracing::error!("compute_visibility_geometry: PlayerCharacter query failed");
         return;
     };
 
@@ -90,6 +91,7 @@ pub fn compute_observer_snapshot(
         cognitive_delay_opt,
     )) = observer_query.single_mut()
     else {
+        tracing::error!("compute_observer_snapshot: PlayerCharacter query failed");
         return;
     };