Add crash-recoverable catalog snapshot and apply - #113

Summary

• add deterministic declaration snapshots and root-CAS whole-catalog apply with source-free recovery
• keep all authoring staging in the retained .st2 control plane and publish through no-follow directory capabilities
• fence unlocked readers with a durable monotonic generation plus recoverable incomplete-generation intent
• preserve marker-time message, status, context, and Resource mutations through a coherent retained-capability address book

Contract

• st2 catalog snapshot --output DIR [--json]
• st2 catalog apply --prepared DIR --expect-sha256 HEX [--json]
• st2 catalog apply --resume [--json]
• st2 agent digest (--spec FILE | --bundle DIR) [--json]
• st2 agent publish ... --input-sha256 HEX

Apply has exactly two closed modes: a new prepared hash-CAS transaction or marker-authorized resume. A durable apply marker protects whole-catalog recovery. Each declaration writer also creates a durable generation intent before mutation; shared readers fail closed on it, and the next exclusive writer conservatively advances the generation and clears an orphan intent.

State traffic remains unlocked. During apply, routing uses the validated original-agent/current-spec union, coherent generation -> marker -> generation sampling, and retained component directory capabilities. No state or declaration mutation follows swapped path ancestors.

Verification

• cargo check --tests
• focused integration: 74/74
  • presentation: 13/13
  • publish: 17/17
  • catalog apply: 28/28
  • task inventory: 10/10
  • message: 6/6
• resource traversal unit: 1/1
• git diff --check
• causal coverage for apply/publish/presentation ABA, post-commit generation failure and recovery, .st2 and declaration ancestor swaps, leaf and identity EXDEV/resume, marker-clear address fencing, and marker-time message/status/context/resource mutations
• final independent read-only review: no P0/P1/P2 findings

This now targets main after #106 merged.