docs: add CLAUDE.md with dev context and coding guidelines reference

CLAUDE.md

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+# OpenDecree Python SDK — Claude Context
+
+## Overview
+
+Python SDK for the OpenDecree configuration service. Wraps the gRPC API with sync and async
+clients, a field-watching subscription layer, and optional OpenTelemetry instrumentation.
+
+## Tech Stack
+
+| Concern | Tool |
+|---------|------|
+| Language | Python 3.10+ |
+| Transport | grpcio |
+| Serialization | protobuf, googleapis-common-protos |
+| Code generation | grpcio-tools (Docker) |
+| Lint / format | ruff |
+| Type checking | mypy |
+| Tests | pytest, pytest-asyncio |
+| Docs | pdoc |
+
+## Development
+
+### Prerequisites
+
+Python 3.10+, Docker (for proto generation), Make.
+
+### Key Commands
+
+```bash
+make generate      # regenerate proto stubs + _constants.py (Docker)
+make lint          # ruff check + format check
+make typecheck     # mypy
+make test          # pytest (unit)
+make integration   # pytest -m integration (requires live server)
+make pre-commit    # lint + typecheck + test
+```
+
+### Layout
+
+```
+sdk/
+├── src/opendecree/   # public package
+│   ├── _generated/   # generated proto stubs (committed)
+│   └── ...
+├── tests/            # unit + integration tests
+└── pyproject.toml
+```
+
+## Coding Guidelines
+
+See [coding-guidelines.md](https://github.com/opendecree/decree/blob/main/docs/development/coding-guidelines.md)
+for the shared philosophy (vanilla principle, minimal deps) and the Python-specific section
+(runtime deps, type annotations, asyncio patterns, ruff enforcement).
+
+## Conventions
+
+- Generated proto stubs live in `sdk/src/opendecree/_generated/` and are committed
+- `_constants.py` is generated from `pyproject.toml` via `build/gen-constants.py`
+- Apache 2.0 license