feat: add uv dependency management with pyproject.toml

[littlewwwhite]

Summary

• Add pyproject.toml with PEP 621 project metadata and pinned dependencies aligned with existing requirements.txt
• Add uv.lock for reproducible dependency resolution
• Add .python-version (3.12) for uv python version pinning
• Update README with uv sync as recommended install method, keeping pip as fallback

Motivation

The project currently only uses a flat requirements.txt for dependency management. Adding uv support provides:

• Reproducible builds — uv.lock locks the full dependency tree, preventing implicit version drift
• Faster installs — uv is 10-100x faster than pip
• Standard metadata — pyproject.toml follows PEP 517/518/621, the modern Python packaging standard
• Backward compatible — existing pip install -r requirements.txt workflow is preserved

Test plan

• uv sync installs all dependencies successfully
• Core imports verified (litellm, pymupdf, PyPDF2, dotenv, yaml)
• uv.lock uses official PyPI registry (no mirror URLs)
• Maintainer review of Python version constraint (>=3.10) and dependency pins

[claude]

Claude Code Review

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