fix(client): revert DIALOGUE_MAX_WIDTH to 1200px (intentional override of D-076)

The 1200px value was a deliberate readability decision, not a spec
violation. Reverts the incorrect 640px change from round 1. Updates
comment and regression test to match.

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

client/scripts/constants.gd

@@ -91,10 +91,10 @@ const FACING_INDICATOR_SIZE: float = 6.0
 const FACING_INDICATOR_OFFSET: float = 14.0
 
 # D-076 (OQ-29 resolution): Dialogue box max-width in pixels.
-# 640px = 20 × TILE_SIZE (32px) — grid-aligned, ~33% of 1920px viewport.
+# Raised from D-076 default (640px) to 1200px for readability.
 # Tyre architecture review 2026-02-19: readability over max-width; fits
 # two columns of text comfortably, leaves world game visible alongside.
-const DIALOGUE_MAX_WIDTH: int = 640
+const DIALOGUE_MAX_WIDTH: int = 1200
 
 # Default camera zoom — used as fallback when get_camera_2d() returns null
 const CAMERA_DEFAULT_ZOOM: Vector2 = Vector2(2.0, 2.0)