feat: DRS chain-viz — delegation chain visualization command

[OkeyAmy]

Problem

Delegation chains can be deep and complex. Without visualization, understanding the delegation path from root to invocation requires manually parsing JWT payloads and tracing issuer/audience relationships.

Proposed Solution

Build a drs chain-viz CLI command that renders a delegation chain as a visual tree or graph.

Acceptance Criteria

• CLI command that accepts a chain bundle (file path or stdin) and outputs a visual representation
• Shows: each receipt as a node with issuer DID (abbreviated), audience DID, command, policy summary
• Shows: chain linkage arrows with hash references
• Output formats: ASCII art (default for terminal), Mermaid diagram (for docs/markdown), DOT (for Graphviz)
• Tests cover: formatting logic for each output format, single-receipt chains, multi-hop chains
• No hardcoded DIDs in tests — use conformance fixtures from fixtures/conformance/receipts/

Relevant Files

• fixtures/conformance/receipts/full-chain-bundle.json — test input
• drs-sdk/src/cli/ — CLI infrastructure
• drs-sdk/src/sdk/types.ts — receipt type definitions

Implementation Notes

ASCII art is the priority output format. Mermaid and DOT can be follow-ups. The command should decode JWT payloads without verifying signatures (verification is the verifier's job, not the visualizer's).