Add event funnels

[tudddorrr]

Event funnel model

• Add an EventFunnel entity storing a name, an ordered list of steps, and a max gap between steps, with a database migration and registration in the entities index.
• Add full CRUD endpoints under /games/:gameId/event-funnels (create, list, get, update, delete) scoped to the game, plus schema validation covering step names, rule operators, and max gap.

ClickHouse funnel computation

• Compute funnel conversion in ClickHouse by joining each step on the previous one for the same player, within the configured max gap and date window.
• Each step reports distinct player count, percentage relative to the first step, and average seconds to reach the next step.
• Support step property rules with operators (set, =, !=, comparison, between, contains) combined in and/or mode, and exclude dev build events unless dev data is requested.
• Add a preview endpoint to evaluate a funnel definition without persisting it.

Caching

• Cache computed funnel results per game, funnel, date window, and dev-data flag with a 15-minute TTL.
• Bust the cache on funnel update and via an explicit refresh endpoint so results stay current.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.42%. Comparing base (953531f) to head (88505bd).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1045      +/-   ##
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+ Coverage    98.37%   98.42%   +0.04%     
===========================================
  Files          467      477      +10     
  Lines         7462     7614     +152     
  Branches       984      999      +15     
===========================================
+ Hits          7341     7494     +153     
  Misses          49       49              
+ Partials        72       71       -1     

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