Add admin stats list route

[tudddorrr]

New admin API endpoint for listing game stats

• Added a GET /admin/v1/game-stats route accessible via admin API keys with the READ_STATS scope.
• The endpoint supports the same query parameters as the existing protected list route: withMetrics, metricsStartDate, and metricsEndDate.

Shared handler extraction

• The game stat list logic was extracted from the protected route handler into a reusable listStatsHandler function.
• Both the protected (dashboard) and admin API routes now delegate to this shared handler, avoiding duplication.

Admin router updates

• Registered the new list route on the game stat admin router.
• Changed the docsKey from 'adminGameStats' to 'GameStatAdminAPI'.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (bd71d50) to head (0bd9977).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1018   +/-   ##
========================================
  Coverage    98.33%   98.33%           
========================================
  Files          439      440    +1     
  Lines         7248     7251    +3     
  Branches       972      972           
========================================
+ Hits          7127     7130    +3     
  Misses          49       49           
  Partials        72       72           

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