Verify: VBP (Verification via Backpropagation) terminology and alias

[ywatanabe1989]

Summary

Introduce BPV (Backpropagation Verification) as the official term for verify_chain's backward-tracing behavior, and add a verify_bpv alias.

Current State

verify_chain already implements BPV — tracing from a target file backward through its dependency chain. The functionality exists; what's missing is the naming and conceptual framing.

Proposed Changes

1. Alias: scitex verify bpv <target> as alias for verify chain
2. Documentation: Position BPV as a named concept — "tracing hash-chain integrity from Claim layer back toward Source layer"
3. Output labeling: Show "BPV trace" in CLI output and Mermaid diagrams

Motivation

• "BPV" is concise and memorable (analogous to backpropagation in deep learning)
• Gives the paper a crisp term for the backward verification concept
• No code change needed for core logic — just naming, aliases, and docs