[idea] Add randomization for AI race, avatar and optionally teams in game setup

[DonBellozi]

Description

When creating a game with AI players, all AI slots are set to the same defaults – Romans race and Octavius avatar. If the player does not manually change every AI slot, the match often ends up with identical opponents, which reduces variety and is easy to overlook during setup.

Suggestion

Add optional automatic randomization for AI parameters during game creation or in the lobby:

• Randomize AI race – assign a random race to each AI player
• Randomize AI avatar – assign a random avatar to each AI player
• (Optional) Randomize teams – randomly distribute players between teams

Expected behavior

• Randomization applies only to AI slots (does not affect human players).

• Executed either automatically on game creation or via a "Randomize" button in the lobby.

• If a race/avatar was manually selected, one of the following behaviors could be used:

  • Keep manual selection unchanged, or
  • Override only if a "Force random" option is enabled.

[Spikeone]

Although this is somewhat a duplicate of #463 - this one is more refined (since this one also takes random portraits into account)