fix: chess — thinner white stroke, coords outside board in border area

- White pieces: 0.5px #444 stroke (subtler outline, looks more solid)
- Coordinates: moved outside board (bottom -22px, left -20px)
- Coords larger (12px), centered, light grey (#aaa)
- Board wrapper: padding for coord space (22px left, 22px bottom)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/css/chessboard.css

@@ -95,6 +95,8 @@
   flex: 1;
   min-width: 0;
   direction: ltr;
+  padding-left: 22px;
+  padding-bottom: 22px;
 }
 
 .board-wrapper::before {
@@ -188,15 +190,15 @@
 
 .piece[data-color="w"] {
   color: #fff;
-  -webkit-text-stroke: 1px #666;
+  -webkit-text-stroke: 0.5px #444;
   paint-order: stroke fill;
-  filter: drop-shadow(1px 2px 1px rgba(0,0,0,0.3));
+  filter: drop-shadow(0 2px 2px rgba(0,0,0,0.35));
 }
 
 .piece[data-color="b"] {
   color: #000;
   -webkit-text-stroke: 0px transparent;
-  filter: drop-shadow(1px 2px 1px rgba(0,0,0,0.2));
+  filter: drop-shadow(0 2px 2px rgba(0,0,0,0.2));
 }
 
 .piece:hover {
@@ -212,45 +214,42 @@
   filter: drop-shadow(0 4px 8px rgba(0,0,0,0.4));
 }
 
-/* Coordinate labels - inside squares */
+/* Coordinate labels - outside board in border */
 .board-coords-file, .board-coords-rank {
   position: absolute;
   display: flex;
   font-family: var(--font-en);
-  font-size: 10px;
+  font-size: 12px;
   font-weight: 700;
   pointer-events: none;
-  z-index: 2;
+  z-index: 6;
 }
 
 .board-coords-file {
-  bottom: 1px;
+  bottom: -22px;
   left: 0;
   right: 0;
 }
 
 .board-coords-file span {
   flex: 1;
-  text-align: right;
-  padding-right: 2px;
-  color: var(--text-3);
-  opacity: 0.8;
+  text-align: center;
+  color: #aaa;
 }
 
 .board-coords-rank {
   top: 0;
   bottom: 0;
-  left: 1px;
+  left: -20px;
   flex-direction: column;
 }
 
 .board-coords-rank span {
   flex: 1;
   display: flex;
-  align-items: flex-start;
-  padding-top: 1px;
-  color: var(--text-3);
-  opacity: 0.8;
+  align-items: center;
+  justify-content: center;
+  color: #aaa;
 }
 
 /* Arrow Canvas */