BCR-004: Prose cleanup and envelope-cli validation

- Reduce document from ~560 to ~289 lines
- Remove verbose explanations, keep direct statements
- Validate all examples with envelope-cli:
  - Signature-with-assertions pattern (BCR-2024-009 style)
  - Wrapped signing for third-party assertions
  - Parallel signatures
  - Counter-signatures
- Both inner and outer signatures verify correctly

Signed-off-by: Christopher Allen <ChristopherA@LifeWithAlacrity.com>

Author: ChristopherA