RivalsData API 1.2.2

Clarifies that the player overview's overall win rate is the current competitive
season's win rate, using the latest available season with usable counts when
there is no direct source rate. It does not aggregate across seasons.

• Updates the Player.win_rate docstring, README, API inventory, and project
  context to explain the season scope.
• Updates MCP overview and dashboard descriptions.
• Labels the dashboard percentage as "season win rate".

Win-rate calculations and the existing per-season/all-seasons hero and class
selectors retain their behavior.

Validation: all 16 tests, Ruff checks, and source/wheel builds pass.