fix(client): free camera review fixes — action toggle, zoom reset, discrete guard, tests (#898)

- Replace raw KEY_F4 check with Input.is_action_just_pressed("free_camera") to
  consume the registered project action (matches F3/F12 dev toggle pattern)
- Reset camera.zoom to Vector2.ONE when toggling free camera off so zoom does
  not bleed into normal gameplay
- Add free_camera_mode guard to InputMapper._unhandled_input() so discrete
  actions (INTERACT, stance, pause) are suppressed alongside movement
- Add client/tests/test_free_camera.gd: flag default, movement suppression,
  discrete action suppression, zoom constant contracts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/scripts/autoloads/input_mapper.gd

@@ -117,6 +117,8 @@ func _process(_delta: float) -> void:
 
 # Discrete actions: fire once on key press (not held).
 func _unhandled_input(event: InputEvent) -> void:
+	if GameState.dialogue_active or GameState.free_camera_mode:
+		return
 	var action: Action = -1
 
 	if event.is_action_pressed("interact"):