feat(psa): add ticket search and status API endpoints

Add three new endpoints under /integrations/psa:
- GET /tickets/search: search CW tickets with query, board_id, status_id filters
- GET /tickets/{ticket_id}: fetch a single ticket by ID
- GET /tickets/{ticket_id}/statuses: get available statuses for a ticket's board

Add PSATicketSearchResult and PSATicketStatusItem schemas.
All endpoints require engineer_or_admin auth.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/schemas/__init__.py

@@ -17,6 +17,7 @@ from .script_template import (
 )
 from .psa_connection import (
     PsaConnectionCreate, PsaConnectionUpdate, PsaConnectionResponse, PsaConnectionTestResponse,
+    PSATicketSearchResult, PSATicketStatusItem,
 )
 
 __all__ = [
@@ -44,4 +45,5 @@ __all__ = [
     "ScriptGenerateRequest", "ScriptGenerateResponse", "ScriptGenerationRecord",
     # PSA Connection
     "PsaConnectionCreate", "PsaConnectionUpdate", "PsaConnectionResponse", "PsaConnectionTestResponse",
+    "PSATicketSearchResult", "PSATicketStatusItem",
 ]