Add approval evidence to cache prune dry-runs

[StatPan]

Goal

Make gira cache prune --dry-run --json emit the shared gira-approval-plan/v1 approval evidence envelope so adapters can approve local cache deletion from a stable plan.

Scope

• Add a stable cache-prune-report/v1 schema version to cache prune JSON reports.
• Preserve apply/dry-run mode in the report and omit approval evidence from apply reports.
• Attach approval evidence to dry-runs with planned cache deletion actions, blockers/warnings arrays, reconstructed commands, and post-apply verification.
• Update the agent-kernel adapter contract gap text after cache prune is covered.

Acceptance Criteria

• Dry-run JSON includes schema_version: cache-prune-report/v1 and approval.schema_version: gira-approval-plan/v1.
• Approval evidence includes planned cache prune actions, stable blockers/warnings arrays, apply/dry-run commands, and post-apply verification.
• Apply JSON retains the schema version and omits dry-run approval evidence.
• Existing cache prune selection/deletion behavior stays compatible.

Expected Delivery

Open one implementation PR with focused tests for core cache prune report construction and CLI JSON output. Merge after checks pass.

Parent: #521

base_branch: main
base_source: branch_policy.default
branch_policy_mode: github-flow
target: default
work_branch: issue-625-add-approval-evidence-to-cache-prune-dry-runs

[StatPan]

Finish Receipt

• Finished at: 2026-05-23T07:00:04Z
• Ticket: Add approval evidence to cache prune dry-runs #625 status=Done state=closed
• Linked PR: feat: Add approval evidence to cache prune dry-runs #626 state=MERGED merged=true
• Checks: passed total=11 passing=11 pending=0 failing=0
• Review: unknown
• Evidence: closing_reference,branch_binding,checks
• AI Delivery Telemetry: not_required
• Label changes: add=status:done remove=status:in-review
• Warnings: missing_acceptance_criteria
• Next: ticket is done