FEAT: add main app base files

FEAT: add main app base files

Context

• Added app.py for the interface and entrypoint logic, i.e. fastAPI, gradio, Dash, Django, or flask.
• Added src with main planned files with the following initial structure:

├── .github/
│   └── workflows/
│       └── ci.yml         # For code quality checks
├── src/
│   └── arxivhound/
│       ├── __init__.py
│       ├── agent.py       # Core agent logic (LangGraph)
│       ├── arxiv_client.py # arXiv API interaction
│       └── summarizer.py  # Summarization logic
├── data/
│   └── .gitkeep
├── app.py                 # Gradio/Dash UI
├── pyproject.toml
├── README.md
├── LICENSE
└── .gitignore