fix(client): address PR #22 review — 3 critical bugs, 2 warnings, 8 suggestions

Critical fixes:
- fog_state: guard _compute_bounds() against all-invalid tiles (negative Rect2i crash)
- fog_shader: read Camera2D zoom dynamically instead of hardcoded Vector2(2,2)
- world_radial: set custom_minimum_size in _ready() from spoke geometry

Warnings:
- fog.gdshader: tighten PERIPHERAL_LOW 0.15→0.55 to match D-059 peripheral band
- Extract color_for_entity_kind() to Constants.gd, decouple CursorRenderer from EntityRenderer

Documentation: shallow copy assumption, gradual decay TODO, tween guard rationale,
fade timing rationale, ToggleInsert TODO, monologue consume-once, hover offset safety,
v6 fixture gap TODO.

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

client/scripts/autoloads/fog_state.gd

@@ -62,6 +62,8 @@ func update_from_state() -> void:
 	var positions: Dictionary = GameState.visible_positions
 	var sectors: Dictionary = GameState.visibility_sectors
 
+	# TODO(v0.2): gradual decay over game-time instead of immediate 255→128
+
 	# 1. Clear visibility, then write current LOS
 	_vis_bytes.fill(0)
 	for pos in positions:
@@ -93,6 +95,7 @@ func update_from_state() -> void:
 	_exp_image.set_data(_width, _height, false, Image.FORMAT_R8, _exp_bytes)
 	exploration_texture.update(_exp_image)
 
+	# Shallow copy — correct for Dictionary<Vector2i, bool/String> values
 	_prev_visible = positions.duplicate()
 
 
@@ -108,5 +111,8 @@ func _compute_bounds(tiles: Array) -> Rect2i:
 		min_y = mini(min_y, int(tile.y))
 		max_x = maxi(max_x, int(tile.x))
 		max_y = maxi(max_y, int(tile.y))
+	# Guard: all tiles invalid (no x/y) — sentinels would produce negative Rect2i
+	if min_x > max_x:
+		return Rect2i(0, 0, 1, 1)
 	# Margin for fog gradient bleed at edges
 	return Rect2i(min_x - 4, min_y - 4, max_x - min_x + 9, max_y - min_y + 9)