feat: add sidebar stats Pydantic schemas

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

backend/app/schemas/sidebar.py

@@ -0,0 +1,45 @@
+"""Schemas for sidebar stats endpoint."""
+
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+
+from pydantic import BaseModel
+
+
+class SidebarActiveSession(BaseModel):
+    """An active or paused session for the activity feed."""
+    session_id: UUID
+    tree_name: str
+    tree_id: UUID
+    tree_type: str
+    started_at: datetime
+    ticket_number: Optional[str] = None
+    psa_ticket_id: Optional[str] = None
+
+
+class SidebarRecentSession(BaseModel):
+    """A recently completed session for the activity feed."""
+    session_id: UUID
+    tree_name: str
+    tree_id: UUID
+    tree_type: str
+    completed_at: datetime
+
+
+class SidebarTreeCounts(BaseModel):
+    """Tree counts for All Flows sub-items."""
+    total: int
+    troubleshooting: int
+    procedural: int
+    maintenance: int
+
+
+class SidebarStatsResponse(BaseModel):
+    """Response for GET /sessions/sidebar-stats."""
+    resolved_today: int
+    active_count: int
+    total_session_minutes_today: int
+    tree_counts: SidebarTreeCounts
+    active_sessions: list[SidebarActiveSession]
+    recent_completions: list[SidebarRecentSession]