v0.3-T5 — ahc diff (structural manifest diff)

[sv-pro]

Summary

Implement ahc diff <manifest-a> <manifest-b> — structural diff between two World Manifest versions showing what changed in actions, taint rules, escalations, and budget limits.

Depends on: #121 (validate)

Scope

• Compare two compiled manifest artifacts (not raw YAML text diff)
• Report: actions added/removed, taint rules changed, escalation conditions changed, budget limits changed
• Human-readable output with +/- markers
• --json flag for machine-readable output

Key Files

• src/agent_hypervisor/compiler/cli.py — add diff command
• tests/compiler/test_diff.py — new test file

Acceptance Criteria

• ahc diff manifests/workspace_v1.yaml manifests/workspace_v2.yaml shows structural changes
• Budget limit changes appear in diff output
• pytest tests/compiler/test_diff.py -v passes

Milestone

v0.3