fix(client): address PR #4 review feedback

Hoshe critical fixes:
- _action_enum_to_wire uses InputMapper.Action constants instead of
  fragile integer literals; OPEN_MENU explicitly handled as client-only
- Remove int() coercion on tick/entity_id — use direct assignment since
  GDScript int is signed 64-bit (safe for realistic tick values)
- Check encode result before buffering in send_input() — reject empty
  bytes instead of corrupting the outbound stream
- Test snapshot now uses Protocol format {tick, entities} instead of
  legacy schema; GameState updated to derive player position from
  entity data; main.gd and world_renderer.gd updated accordingly

Hoshe warnings:
- 5 negative tests added (truncated bytes, wrong type, missing fields,
  empty bytes, encode validation) — 20/20 tests pass
- receive_bytes signal is emitted at consume time in poll_snapshot by
  design (documented in code)

Tyre suggestions:
- Remove duplicated root-level fixtures — single source of truth in
  client/tests/fixtures/msgpack/
- gen_fixtures.rs writes directly to client/ directory
- Add `make fixtures` target for regeneration

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

client/scripts/main.gd

@@ -24,16 +24,6 @@ func _process(_delta: float) -> void:
 		# Track camera to player position (D-015)
 		camera.position = GameState.player_position * 32  # tile-space to pixel-space
 
-		# Update HUD
-		if hud and hud.has_method("update_from_hud_data"):
-			hud.update_from_hud_data(GameState.hud_data)
-			if snapshot.has("player") and snapshot.player.has("health"):
-				hud.update_health(snapshot.player.health)
-
-		# Wire monologue display (D-016 perception data path)
-		if snapshot.has("monologue") and monologue_display:
-			monologue_display.show_monologue(snapshot.monologue)
-
 	# Send queued input to simulation
 	var inputs = InputMapper.flush_queue()
 	for input in inputs: