fix(S15P11A705-14): require ticket descriptions

[tpals0409]

Summary

• reject missing or whitespace-only draft ticket descriptions before persistence
• reject confirm when preview is not ready or contains a legacy blank description
• require a non-empty description in the Jira MCP create bridge before discovery or dispatch

Jira

S15P11A705-14

TDD Evidence

RED: .venv/bin/pytest -q tests/test_api.py::test_submission_requires_preview_confirmation_before_ticket_creation failed because a null description returned HTTP 200, exit=1

GREEN: .venv/bin/pytest -q tests/test_api.py::test_submission_requires_preview_confirmation_before_ticket_creation tests/test_mcp_create_bridge.py passed focused API and pre-dispatch bridge tests, exit=0

Regression: .venv/bin/pytest -q passed the full 37-test suite, exit=0

Additional verification

• .venv/bin/ruff check app tests passed
• compileall, git diff check, Docker build, and MCP OAuth import passed
• no Jira issue was created during verification