feat(theme): add four Claude-branded chess piece sets

[jhonnold]

Summary

Adds four new in-repo chess piece sets to the Theme → Pieces selector:

• Claude — Staunton-style silhouette; king carries a coral 4-point asterisk on the body.
• Claude Minimal — Flat geometric primitives (circles, rects, polygons) with a single coral accent per piece.
• Claude Glyph — Typographic: each piece is its SAN letter (K/Q/R/B/N/P) in bold Georgia over a coral underline.
• Claude Playful — Rounded cartoony silhouettes (pawn has coral cheeks, knight a coral eye + smile, king a coral star).

All 48 SVGs are hand-written (no upstream source), share the coral accent #D97757, and use the classic 45×45 viewBox so they scale identically to the existing sets — no meridian-style scaling shim needed.

Registry: public/js/components/theme/piece-sets.ts PieceSetId union and PIECE_SETS array extended with the four new entries. Every consumer (board/, theme modal, pieceSrc()) already reads from this registry, so no other code changes were required. DEFAULT_PIECE_SET stays 'classic', so the pre-JS fallback path in views/pages/broadcasts.ejs is unaffected. public/img/pieces/CREDITS.md updated with attribution.

Test plan

• npm run build (TypeScript + webpack) clean
• Backend live test against broadcast 16065 with dev-server + dev-public
• Theme → Pieces dropdown lists 8 sets in declared order
• Each of the 4 new sets renders all 12 pieces on the main board with a visible coral accent
• Mini-boards (Games tab) and Replay view honor the selected set
• localStorage.tlcv.pieceSet persists across reloads
• Existing 4 sets (classic, livius, meridian, meridian_shaded) unchanged