chore(pm): vendor the Aramesh/PM platform under pm/ (squash of Aramesh/PM @ 91f3271)

The PM panel (PmPanelPage -> iframe /pm/) needs the project-management
platform served at /pm/ on the ERP domain. Source: org repo Aramesh/PM,
branch feature/project-management-platform. Update via:
git subtree pull --prefix=pm aramesh-pm feature/project-management-platform --squash

pm/backend/requirements.txt

@@ -0,0 +1,14 @@
+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+sqlalchemy[asyncio]==2.0.36
+asyncpg==0.30.0
+pydantic==2.10.4
+pydantic-settings==2.7.0
+httpx==0.28.1
+python-multipart==0.0.20
+alembic==1.14.0
+pytest==8.3.4
+pytest-asyncio==0.24.0
+aiosqlite==0.20.0
+
+pyjwt[crypto]>=2.8.0