Heroes vs. Villains: stage 1 and 3 music could fit the game better #98

The stage music for The Generation Floor (stage 1) and The Agentic Core (stage 3) in Heroes vs. Villains could match the game more closely. The Review Gauntlet (stage 2) and the boss tracks aren't part of this issue.

Tracks

• Assets/Audio/Beat'em Up/Hero vs Villian/heroes_villains_generation_floor.ogg
• Assets/Audio/Beat'em Up/Hero vs Villian/heroes_villains_agentic_core.ogg

Both are wired up in modes/beatem_up/reinvent/catalog.gd (MUSIC).

Done when both tracks fit their stage's look and pace as well as the stage 2 track does. Each stage track should still loop after its intro, and the boss-music dip and swap should keep working (covered by tests/heroes_villains_logic.gd). If a track is replaced, update its credit.

Noted while reviewing #97.