AKUNUR 2.10.3 - BOARD DESIGN TEST BUILD

Purpose
- Experimental derivative of the supplied 2.10.3 build.
- Rules and gameplay logic remain at 2.10.3.
- Adds stable SVG classes and data attributes for board-design experiments.

Live board appearance options
- Standard board
- Subtle ring shading
- Ring boundaries
- Shading + boundaries

The appearance selector is under Game settings. It applies immediately and is
remembered in local storage. The default for a new browser is Subtle ring shading.

CSS-only experimentation
- Board appearance rules are isolated in board-theme.css.
- Uploading a replacement board-theme.css changes board design without rebuilding
  the JavaScript package. A hard refresh may be needed if the web server/browser
  caches the old stylesheet.
- The variables at the top of board-theme.css control the main tones and line widths.

Cell classes
- board-cell
- ring-0 through ring-9 (depending on board radius)
- ring-even / ring-odd
- cell-normal / cell-corner / cell-still-point
- inner-ring / outer-ring
- principal-axis, axis-q-zero, axis-r-zero, axis-s-zero
- is-placement-zone / is-last-move / is-selected / is-echo-highlight

Cell data attributes
- data-cell-q / data-cell-r (existing click targets)
- data-q / data-r / data-s
- data-ring
- data-cell-type
- data-echo-q / data-echo-r

Boundary classes
- board-ring-boundary
- ring-boundary-1 etc.
- ring-boundary-even / ring-boundary-odd
- outer-board-boundary

Implementation note
- Ring boundaries are exact shared-edge overlays generated from board geometry.
  They do not merely thicken every hex in an alternate ring.
