[#117]: Document and test MessageDisplay hook event compat (v2.1.152)

[delexw]

Summary

Claude Code v2.1.152 introduces a new MessageDisplay hook event. This PR confirms that the parser already handles it correctly and adds explicit documentation and tests to prove it.

Root cause analysis

• hook_event in Entry is stored as a plain String (not an enum), so new hook event names are captured without rejection or a code change.
• All classify paths in classify.rs rescue hook entries based on the presence of a hookEvent field, not an exhaustive match — so MessageDisplay flows through as a ClassifiedMsg::Hook automatically.
• UUID gaps from hidden messages (if a MessageDisplay hook omits an entry from JSONL entirely) are handled gracefully by the _ => break arm in resolve_live_chain_uuids, which terminates the backward chain walk without panicking.

Changes

src-tauri/src/parser/entry.rs

• Added a comment on the hook_event field documenting that it is stored as a plain String for forward compatibility (v2.1.152+ MessageDisplay included).
• Added 2 new tests: parse_entry_captures_message_display_hook_event_as_string and parse_entry_message_display_as_attachment_is_captured.

src-tauri/src/parser/classify.rs

• Added 3 new tests covering MessageDisplay in all three entry shapes:
  • classify_message_display_progress_entry_produces_hook_msg
  • classify_message_display_system_hook_progress_entry_produces_hook_msg
  • classify_message_display_attachment_entry_produces_hook_msg

src-tauri/src/parser/session.rs

• Added a comment in resolve_live_chain_uuids explaining the uuid gap assumption for MessageDisplay-hidden entries and how the _ => break arm handles it gracefully.

specs/01-parser-pipeline.md

• Added a MessageDisplay row to the Version-Compatibility Normalisations table.

Test results

• vitest: 349 tests passed
• cargo test: 375 tests passed (includes 5 new tests)
• cargo clippy -- -D warnings: clean

Fixes #117