Add replayable WordPress runtime snapshot bundles

[chubes4]

Problem

Runtime snapshots are currently useful metadata, but they are not yet complete replayable WordPress state. First-class eval/replay consumers need a snapshot that can reconstruct enough of the runtime to rerun graders and inspect failures later.

Current replay notes are intentionally partial: mounted text files can be replayed, while DB state, uploads, active theme/plugins, options, media, and browser/editor state are not fully captured.

Scope

Define a replayable WordPress runtime snapshot bundle that can include:

• database or Playground state export
• posts/options/terms/users where supported
• active theme/plugins
• uploads/media references
• mounted files, including binary-safe handling
• generated blueprint/replay instructions
• replay limitations manifest
• snapshot digest and artifact refs

Use explicit semantics such as metadata-only, partial-replay, and replayable-runtime-state.

Non-goals

• Do not score, grade, or interpret task success.
• Do not make private site export implicit; snapshot capture must remain policy-controlled.

Acceptance criteria

• A runtime can emit a snapshot artifact with clear replay semantics and limitations.
• Snapshot artifacts are listed in the bundle manifest with SHA-256 verification.
• Runtime episode trace snapshot refs point to the emitted artifact when present.
• Smoke coverage proves metadata-only behavior remains valid and replayable snapshots verify when requested.