refactor(simulation): address PR #32 review — 14 items from Hoshe + Tyre

Hoshe (code quality):
- Remove dead RoomMember component from reset.rs
- Remove execute_reset (dual API trap); plan_reset is sole production path
- .unwrap() → .expect() on reset_plate in setup_gauntlet boot path
- Add 10s read timeout to TCP runtime test (prevents hangs)
- Register player in EntityRegistry in runtime boot test
- Document room_at z-range and corridor overlap assumptions
- Derive entity count from EXPECTED_ENTITY_COUNT constant (was hardcoded 24)
- Add reset plate (49-51) verification to stable_id_ranges_match_spec
- Add debounce exact boundary test (tick 9 rejected, tick 10 accepted)

Tyre (architecture):
- Gate test_world rooms/constants/setup behind "gauntlet" feature (default-on);
  reset module stays always-compiled (production dependency via input system)
- Document setup_gauntlet scheduler bypass for future tracking
- Extract runtime TCP test to content_runtime.rs (separate failure modes)

507 tests passing.

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

server/src/main.rs

@@ -116,7 +116,13 @@ fn main() {
 
     // Gauntlet test world for --test-mode, proof room for normal mode.
     if test_mode {
+        #[cfg(feature = "gauntlet")]
         settled_reach_server::test_world::setup_gauntlet(&mut app);
+        #[cfg(not(feature = "gauntlet"))]
+        {
+            eprintln!("--test-mode requires the 'gauntlet' feature");
+            std::process::exit(1);
+        }
     } else {
         setup_proof_room(&mut app);
     }