Add API-key based game webhooks for turn and phase changes

[BullX92]

Supersedes #5166 with a smaller first webhook implementation focused on turn and phase changes.

Summary

• add API-key authenticated per-game webhook subscriptions
• add public webhook event metadata for TURN_CHANGED and PHASE_CHANGED
• persist webhook users and subscriptions with server-owned callback URLs
• dispatch webhook POSTs asynchronously with timeout and transient retry handling
• wire turn and phase notifications into existing game flow paths
• block FoW games from webhook subscription and dispatch

API

• GET /api/public/game/webhook/eventTypes
• PUT /api/public/game/{gameId}/webhook with X-API-Key and { "eventTypes": [...] }
• DELETE /api/public/game/{gameId}/webhook with X-API-Key

Validation

• mvn "-Dmaven.repo.local=C:\00_GIT_Repos\00_TI4_Agent\TI4_AI_Assisstend\tools\m2-repository" -DskipTests "-Dspotless.check.skip=true" compile

Note: normal mvn compile currently stops at Spotless due existing CRLF formatting issues in unrelated files plus formatter changes that should be handled separately to avoid broad formatting churn in this PR.