feat(tickets): allow reopening closed tickets

[Sayrix]

Closes #583.

Adds a staff-only reopen workflow through /reopen and the closed-ticket summary button.

• Restores participant permissions and the active ticket category.
• Re-enables ticket actions while preserving claim state.
• Guards against concurrent reopen attempts and restores the closed database state if Discord updates fail.
• Adds localized feedback and audit logging.
• Prevents delayed transcript uploads from attaching to reopened tickets.