Refactor backend to SQLModel; reset schema; add Company OS endpoints

backend/app/models/__init__.py

@@ -1,2 +1,17 @@
-# Import models here so Alembic can discover them
-from .task import Task  # noqa: F401
+from app.models.org import Department, Employee
+from app.models.projects import Project, ProjectMember
+from app.models.work import Task, TaskComment
+from app.models.hr import HeadcountRequest, EmploymentAction
+from app.models.activity import Activity
+
+__all__ = [
+    "Department",
+    "Employee",
+    "Project",
+    "ProjectMember",
+    "Task",
+    "TaskComment",
+    "HeadcountRequest",
+    "EmploymentAction",
+    "Activity",
+]