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

backend/requirements.txt

@@ -1,26 +1,7 @@
-alembic==1.18.3
-annotated-doc==0.0.4
-annotated-types==0.7.0
-anyio==4.12.1
-click==8.3.1
-fastapi==0.128.0
-greenlet==3.3.1
-h11==0.16.0
-httptools==0.7.1
-idna==3.11
-Mako==1.3.10
-MarkupSafe==3.0.3
-psycopg2-binary==2.9.11
-pydantic==2.12.5
-pydantic-settings==2.12.0
-pydantic_core==2.41.5
-python-dotenv==1.2.1
-PyYAML==6.0.3
-SQLAlchemy==2.0.46
-starlette==0.50.0
-typing-inspection==0.4.2
-typing_extensions==4.15.0
-uvicorn==0.40.0
-uvloop==0.22.1
-watchfiles==1.1.1
-websockets==16.0
+fastapi
+uvicorn[standard]
+sqlmodel
+alembic
+psycopg2-binary
+python-dotenv
+pydantic-settings