Refactor requirements files to remove version pinning for better flexibility in dependency management; add dev-only dependencies in a new requirements-dev.txt file.

Co-authored-by: Copilot <copilot@github.com>

backend/requirements.txt

@@ -1,47 +1,20 @@
-annotated-doc==0.0.4
-annotated-types==0.7.0
-anyio==4.13.0
-backports.asyncio.runner==1.2.0
-bcrypt==3.2.2
-blinker==1.9.0
-certifi==2026.4.22
-cffi==2.0.0
-click==8.3.3
-colorama==0.4.6
-cryptography==47.0.0
-dnspython==2.8.0
-duckdb==1.5.2
-ecdsa==0.19.2
-email-validator==2.3.0
-exceptiongroup==1.3.1
-fastapi==0.136.1
-Flask==3.1.3
-gunicorn==23.0.0
-h11==0.16.0
-httpcore==1.0.9
-httpx==0.28.1
-idna==3.13
-iniconfig==2.3.0
-itsdangerous==2.2.0
-Jinja2==3.1.6
-MarkupSafe==3.0.3
-packaging==26.2
-passlib==1.7.4
-pluggy==1.6.0
-pyasn1==0.6.3
-pycparser==3.0
-pydantic==2.13.3
-pydantic_core==2.46.3
-Pygments==2.20.0
-pytest==9.0.3
-pytest-asyncio==1.3.0
-python-dotenv==1.2.2
-python-jose==3.5.0
-rsa==4.9.1
-six==1.17.0
-starlette==1.0.0
-tomli==2.4.1
-typing-inspection==0.4.2
-typing_extensions==4.15.0
-uvicorn==0.46.0
-Werkzeug==3.1.8
+anyio
+bcrypt
+blinker
+certifi
+cryptography
+dnspython
+duckdb
+ecdsa
+email-validator
+fastapi
+httpcore
+httpx
+Jinja2
+MarkupSafe
+packaging
+passlib
+pydantic
+python-dotenv
+python-jose
+uvicorn