Real-time conversation viewer

Every bot now has a Conversations tab that shows full thread history. What's there:

• Paginated thread list with search across all messages
• Per-turn citation badges — each assistant message shows which source chunks it drew from, linked back to the source detail page
• Metadata sidebar — model used, token counts, refusal flags, and whether any response was marked as a hallucination by the refusal guard
• Export — download any conversation as JSON or Markdown
• Share link — a copyable URL that opens the thread read-only (useful for pasting into a support ticket)
• Delete — hard-deletes the thread and all its messages

The viewer was previously a rough prototype. This is the production shape.

Commit: 0d7c681