Add opt-in instruction context to Pony Trail snapshots

[0xroylee]

Summary

• Add opt-in instruction_context capture to snapshot entries in both the shell and Python helpers
• Record hashed instruction files, skill metadata, and compact git/session context without storing prompt or file contents
• Surface instruction context in snapshot history output and update runtime parsing, tree rendering, and tests

Testing

• Added unit coverage for snapshot recording, parsing, and history display of instruction context
• Added shell helper tests for opt-in capture and schema-compatible Python fallback behavior

[0xroylee]

@caioribeiroclw-pixel adding you as a participant here.