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/psa_connection.py

@@ -45,3 +45,22 @@ class PsaConnectionTestResponse(BaseModel):
     success: bool
     message: str
     server_version: str | None = None
+
+
+# ── Ticket search & status schemas ────────────────────────────────
+
+
+class PSATicketSearchResult(BaseModel):
+    id: str
+    summary: str
+    company_name: str | None = None
+    board_name: str | None = None
+    status_name: str | None = None
+    priority_name: str | None = None
+    closed: bool = False
+
+
+class PSATicketStatusItem(BaseModel):
+    id: int
+    name: str
+    is_closed: bool = False