Re-scope RIMS as a generic inventory and collection framework

[fusion94]

Description

RIMS needs a clear product and architectural definition. It should be positioned as the shared framework for inventory and collection-oriented systems, not as a one-off electronics inventory app and not as a universal framework for arbitrary applications.

This issue defines what RIMS is for, what kinds of apps it should support, and what it explicitly should not try to become.

This should align with the Brain ADR on RIMS framework direction and provide a durable source of truth for future architectural decisions.

Acceptance Criteria

• Document RIMS purpose as a collection and inventory framework
• Document supported domain examples, such as firearms, wine, sports cards, and collectibles
• Document explicit non-goals, including universal app framework ambitions
• Define the core problem RIMS is intended to solve
• Add or update README and/or architecture docs to reflect this direction
• Ensure terminology is neutral and not tied to electronics inventory