Increased contrast of letter connections for readability.

Bumped the board connection line color in both themes so the links
between letters read more clearly:
- light: #e2dbc7 -> #c7bb95
- dark:  #33333f -> #52525f

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

zangramru/static/index.html

@@ -417,13 +417,13 @@
             light: {
                 tile: '#ffffff', border: '#14110c', shadow: '#14110c',
                 ink: '#14110c', inkOn: '#14110c',
-                line: '#e2dbc7', sel: '#14110c', found: '#12b886', bonus: '#ff7a00', selTile: '#ff3d81',
+                line: '#c7bb95', sel: '#14110c', found: '#12b886', bonus: '#ff7a00', selTile: '#ff3d81',
                 msgDefault: '#c98a00', muted: '#6f6650',
             },
             dark: {
                 tile: '#262633', border: '#f4efe3', shadow: '#000000',
                 ink: '#f4efe3', inkOn: '#14110c',
-                line: '#33333f', sel: '#f4efe3', found: '#24d38a', bonus: '#ffa733', selTile: '#ff479a',
+                line: '#52525f', sel: '#f4efe3', found: '#24d38a', bonus: '#ffa733', selTile: '#ff479a',
                 msgDefault: '#ffd400', muted: '#9a927f',
             },
         };