feat(adventures): add The Brass Heart Gambit heist scenario

- Complete level 5-7 adventure featuring multi-faction heist
- Heart of Harmonic Resonance artifact as central objective
- 5 rival teams with different approaches and motivations
- Multiple infiltration routes: social, stealth, distraction, inside job, legal
- Awakening artifact complications and political intrigue
- Extensive cross-references to Valdris lore and factions

Completes Adventures folder with 5 ready-to-run scenarios covering levels 3-9.

Author: jonathanirvin-ast