feat(approaches): Deepen persona POVs #137

Context

Approaches already have business/technical/legal TLDRs. These need to be substantive enough that the guide frontend can project them as institutional-language content — but the map itself stays in map language.

Scope (all 10 approaches)

• Keep existing persona categories, with legal broadened to legal/risk:
  • Business: throughput, capital efficiency, privacy guarantees, operational impact
  • Technical: SDKs, open source maturity, deployment path, threat models
  • Legal/Risk: regulatory mapping, compliance requirements, jurisdiction specifics, ZK guarantees, visibility tables
• Deepen each POV from bullet-point TLDRs to substantive sections
• Add decision matrix or comparison table where multiple architectures compete
• Map keeps its current structure and wording; "case study" framing is a frontend/guide concern (Track 2)

Done when

All 10 approaches have multi-paragraph persona POVs (not just bullet TLDRs) and at least one decision matrix.