visual redesign: landing, dashboard overview, session calendar (2.3.1)

- Redesign landing page hero with split layout, features section, and in-app session/result demos
- Add fixed sidebar scroll isolation (app-shell overflow lock pattern)
- Redesign leagues index cards with initial badge, podium leader chips, and action links
- Redesign league dashboard: color-coded nav tiles, cash/stats overview strip, session history heatmap calendar
- Dashboard cash stats use real cash only (excludes rollovers and carry-ins)
- Session history calendar: JS-driven full-year grid, year navigation, hover tooltips, full-width responsive layout
- Bump leaderboard tile color from gold to blue (distinct from ledger orange)
- Bump version to 2.3.1

config.py

@@ -9,7 +9,7 @@ DATA_PATH = BASE_DIR / "data" / "entries.csv"
 DEFAULT_DATABASE_URL = f"sqlite:///{BASE_DIR / 'data' / 'boker-dev.sqlite3'}"
 
 ELIGIBLE_MIN_SESSIONS = 3
-APP_VERSION = "2.3.0"
+APP_VERSION = "2.3.1"
 
 
 def load_local_env(env_path: Path) -> None: