v0.8.3 — get_conversation no longer hides reopen replies & screenshots

Fix

get_conversation's slim view previously kept only comment / note / quick_reply parts, silently dropping two part types that carry real content:

• open — customer email replies that reopen a closed conversation (the most recent follow-up, often with screenshots)
• assignment — the first admin reply (frequently sent together with the assignment)

It also stripped all attachments. The result: CS triage (incl. subagents) missed the latest customer message, prior replies, and screenshots — leading to inaccurate responses.

What changed

• Keeps any open / assignment part that carries a real body or attachments from a user/admin author (isMessageBearingPart), while still filtering pure system events.
• Surfaces per-part attachments (name / url / content_type) so screenshots are visible.
• Lifts ticket-form content into explicit ticket.title / ticket.description (previously buried under the internal _default_title_ / _default_description_ keys).
• Drops empty-array ticket attributes.

Verified live against real reopened conversations: previously-dropped open/assignment message parts and their attachments now appear; pure system events stay filtered.

Full diff: v0.8.2...v0.8.3