Publish financial intelligence architecture review

[codeforester]

Summary

• Add the financial intelligence vision, source architecture spec, AssetBuddy design notes, and reviewed architecture proposal under docs.
• Record accepted v2 decisions: keep bankbuddy, use Document/Entity/Observation/Relationship as the foundation, use BB_ singular tables, minimize JSON, pause issue Add tax profile gap detection and annual summary #100, and start net-worth reporting with native-currency buckets.
• Update README and AI context so the new architecture direction is discoverable.

Validation

• git diff --check
• git diff --cached --check
• ./tests/validate.sh

Closes #120