📝 update CHANGELOG for Issue #16 overlay opacity

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

CHANGELOG.md

@@ -7,6 +7,10 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
 
+### Added
+- **Overlay Opacity Setting** (Issue #16): all UI overlay backgrounds (build menu, villager panel, context menu, ESC menu, confirm dialog, Nisse info panel, debug panel) now use a central `uiOpacity` value instead of hardcoded alphas
+- **Settings Screen**: ESC menu → Settings now opens a real overlay with an overlay-opacity row (− / value% / + step buttons, range 40 %–100 %, default 80 %); setting persisted in `localStorage` under `tg_ui_settings`, separate from game save so New Game does not wipe it
+
 ### Added
 - **Unified Tile System** (Issue #14):
   - Tree seedlings: player plants `tree_seed` on grass/dark-grass via the F-key farming tool; seedling grows through two stages (sprout → sapling → young tree, ~1 min each); on maturity it becomes a FOREST tile with a harvestable tree resource