test: 81 unit tests for tickets (data, storage, transcript, ui)

- tests/test_data.py: models serialization, enums, roundtrip
- tests/test_storage.py: CRUD JSON, cache, persistence
- tests/test_transcript.py: HTML generation, escaping, attachments
- tests/test_ui.py: button callbacks with mocked interactions
- Fixed: transcript.py attachments access (dataclass not dict)

tickets/transcript.py

@@ -24,7 +24,7 @@ def generate_transcript(ticket: TicketData, guild_name: str = "") -> str:
         badge = '<span class="badge badge-staff">STAFF</span>' if msg.is_staff else ""
 
         att_html = ""
-        for att in msg.get("attachments", []) if hasattr(msg, "attachments") else msg.attachments:
+        for att in msg.attachments:
             if any(att.lower().endswith(ext) for ext in (".png", ".jpg", ".jpeg", ".gif", ".webp")):
                 att_html += f'<div class="attachment"><img src="{html.escape(att)}" /></div>'
             else: