fix: surface ticket creation failures to the client

[bensofficial]

Summary

• Ticket creation errors were caught and swallowed on the server, so the client received 201 Created and rendered "submitted successfully" even when the ticket system had failed.
• The DB row now stays uncommitted (db.flush() instead of db.commit()) until the ticket succeeds. On a raised exception or a missing key from an enabled ticket system, a new shared helper (api/routes/_ticket.py) rolls back the pending INSERT and raises HTTPException(502) so the client's existing handleSubmissionFailure flow shows the red error toast.
• Applied to all 5 request routes: support, VM, VM access, Artemis developer, TUM guest. NoOp is still tolerated (returns None and ticket_system_enabled is false).

Test plan

• Run uv run ruff check . and uv run ty check . in server/ — I couldn't run these locally (uv not installed).
• Run the Playwright e2e suite — debug ticket system always returns a key, so behavior should be unchanged for happy paths.
• Manually verify: point at a broken Jira/Redmine (or temporarily raise inside handle_support_ticket_creation) and submit a support request. Expect the red "Submission failed" toast, not the green success card.
• Manually verify happy path across each form still works end-to-end (request submitted, ticket created, ticket URL rendered on success card).

🤖 Generated with Claude Code