ttl: add cache lifecycle tooling (inspect/prune/gc)

[kdy1]

Summary

ttlc currently lacks operator-facing cache lifecycle commands for inspection, pruning, and garbage collection.

Evidence

Contract Evidence:

• docs/project-ttl.md:200
• docs/project-ttl-language.md:236

Current Gap

ttlc currently lacks operator-facing cache lifecycle commands for inspection, pruning, and garbage collection.

Proposed Scope

• Not documented yet.

Acceptance Criteria

• Add cache lifecycle command surface (inspect/prune/gc) under ttlc CLI.
• Define deterministic prune/gc policies and safety checks.
• Expose clear machine-readable output aligned with existing envelope style.
• Cover lifecycle command behavior with command-level tests.

Test Scenarios

• Inspect command reports cache metadata and size/count basics.
• Prune removes stale rows according to policy.
• GC cleans orphaned blob artifacts without removing live references.

Out of Scope

• Remote cache administration.
• UI dashboards for cache operations.