Add generic Dynamo agent proxy

[Aphoh]

Summary

• add a standalone Python dynamo-agent-proxy package installable with uv pip install from this repository
• inject nvext.agent_context / nvext.agent_hints for OpenAI /v1/chat/completions and /v1/responses passthrough requests
• add Anthropic /v1/messages compatibility by translating requests to Dynamo /v1/chat/completions and translating non-streaming/streaming responses back to Anthropic shapes
• keep the proxy dependency-light and agent-agnostic; no Pi plugins are required and the package uses the Python standard library at runtime
• preserve unknown existing nvext fields while making proxy-provided context and hint keys authoritative
• document generic proxy install/usage and add Python unit tests
• keep the existing Pi TypeScript provider package metadata unchanged

Review notes

• removed unused code and single-use helpers, and simplified Anthropic text conversion to reduce the proxy implementation
• stripped compressed/duplicate request headers on rewritten JSON bodies and passed Anthropic upstream errors through before stream translation
• scanned the changed Python package for risky process/file execution APIs such as subprocess, eval, exec, os.system, pickle, ctypes, and temp-file creation; none are used

Test plan

• PYTHONPATH=python python3 -m unittest discover -s test/python
• python3 -m py_compile python/dynamo_agent_proxy/proxy.py python/dynamo_agent_proxy/__init__.py python/dynamo_agent_proxy/__main__.py test/python/test_agent_proxy.py
• python3 -m pip wheel . --no-deps --no-build-isolation -w /tmp/dynamo-agent-proxy-wheel-review
• install package in a temporary venv and run dynamo-agent-proxy --help
• npm run check
• npm test
• npm run build