fix: chess coords inside squares like Chess.com, clean board edge

Coordinates now inside squares with contrasting colors:
- Rank numbers: top-left of left column, alternating light/dark
- File letters: bottom-right of bottom row, alternating dark/light
- No separate border/padding needed
- Board: no thick border, just subtle shadow
- Clean minimal look matching Chess.com mobile
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/css/chessboard.css

@@ -95,8 +95,6 @@
   flex: 1;
   min-width: 0;
   direction: ltr;
-  padding-left: 22px;
-  padding-bottom: 22px;
 }
 
 .board-wrapper::before {
@@ -122,13 +120,12 @@
   grid-template-rows: repeat(8, 1fr);
   width: 100%;
   height: 100%;
-  border-radius: 6px;
+  border-radius: 4px;
   overflow: hidden;
   user-select: none;
   touch-action: none;
   direction: ltr;
-  box-shadow: 0 4px 20px rgba(0,0,0,0.5), 0 1px 4px rgba(0,0,0,0.3);
-  border: 3px solid #3d3d3d;
+  box-shadow: 0 2px 10px rgba(0,0,0,0.4);
 }
 
 .square {
@@ -214,42 +211,55 @@
   filter: drop-shadow(0 4px 8px rgba(0,0,0,0.4));
 }
 
-/* Coordinate labels - outside board in border */
+/* Coordinate labels - inside squares like Chess.com */
 .board-coords-file, .board-coords-rank {
   position: absolute;
   display: flex;
   font-family: var(--font-en);
-  font-size: 12px;
+  font-size: 11px;
   font-weight: 700;
   pointer-events: none;
   z-index: 6;
 }
 
 .board-coords-file {
-  bottom: -22px;
+  bottom: 2px;
   left: 0;
   right: 0;
 }
 
 .board-coords-file span {
   flex: 1;
-  text-align: center;
-  color: #aaa;
+  text-align: right;
+  padding-right: 3px;
+}
+
+.board-coords-file span:nth-child(odd) {
+  color: var(--board-dark);
+}
+.board-coords-file span:nth-child(even) {
+  color: var(--board-light);
 }
 
 .board-coords-rank {
   top: 0;
   bottom: 0;
-  left: -20px;
+  left: 2px;
   flex-direction: column;
 }
 
 .board-coords-rank span {
   flex: 1;
   display: flex;
-  align-items: center;
-  justify-content: center;
-  color: #aaa;
+  align-items: flex-start;
+  padding-top: 2px;
+}
+
+.board-coords-rank span:nth-child(odd) {
+  color: var(--board-light);
+}
+.board-coords-rank span:nth-child(even) {
+  color: var(--board-dark);
 }
 
 /* Arrow Canvas */