Adds database-backed TerminalSession model with ACTIVE/CLOSED status enum,
migration SQL, TerminalSessionService (create/findByWorkspace/close/findById),
DTO file with class-validator decorators, unit tests (12 tests), and module
registration. Workspace relation and indexed columns enable efficient session
listing and recovery.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
