Invoice Search FastAPI

This adds a small FastAPI wrapper around the existing INVOICE.PY utilities.

Endpoints:

• POST /upload - upload a PDF file; it will be indexed (one embedding per doc) and a parsed JSON file saved.
• GET /search?q=... - run a semantic search and return top hits.

How to run (dev):

1. Ensure dependencies are installed (prefer the project's venv):

pip install -r requirements.txt

2. Ensure your GOOGLE_API_KEY is available:

• Create a .env file at the project root with GOOGLE_API_KEY=... (the app loads it automatically), or export it in your shell.

3. Start the server:

uvicorn app:app --reload --host 0.0.0.0 --port 8000

4. Open the API docs at http://localhost:8000/docs to upload or search.

Notes:

• If chromadb or the generative API is not available, the app falls back to a local JSON index and a hash-based embedding.
• Do not commit .env — it's in .gitignore.