Add admin stats update route

[tudddorrr]

Admin API for updating game stats

• Added a new PUT /admin/v1/game-stats/:id endpoint allowing admin API keys with the write:stats scope to update game stat properties.
• Introduced loadStat middleware for admin routes that resolves a stat by ID scoped to the admin key's game, returning 404 if not found.

Shared update logic across route tiers

• Extracted the stat update handler into a reusable updateStatHandler function that accepts an EntityManager, stat, validated body, and actor (either a User or AdminAPIKey).
• Both the protected (dashboard) and admin API update routes now delegate to this shared handler, reducing duplication.

Deferred cache invalidation

• Replaced inline clearStatIndexResponseCache middleware with a deferClearResponseCache call inside the shared handler, deferring the cache clear until after the database flush succeeds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (630a7df) to head (f0287c0).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1019      +/-   ##
===========================================
+ Coverage    98.31%   98.33%   +0.01%     
===========================================
  Files          440      442       +2     
  Lines         7251     7261      +10     
  Branches       972      973       +1     
===========================================
+ Hits          7129     7140      +11     
  Misses          49       49              
+ Partials        73       72       -1     

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