docs: add CLAUDE.md with modern-python org conventions

CLAUDE.md

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+# modern-python org conventions
+
+This repo (`modern-python/.github`) builds the org site at **modern-python.org**
+(MkDocs Material, in `docs/`) and hosts the org profile shown on the GitHub org page
+(`profile/README.md`). The conventions below apply across **all** repos in the
+`modern-python` org, not just this one.
+
+## Naming & branding
+
+- Brand/framework casing — use exactly: `modern-di`, `that-depends`, `Litestar`
+  (not "LiteStar"), `FastStream`, `FastAPI`, `Typer`, `SQLAlchemy`, `PostgreSQL`.
+- Per-project docs sites live at `<name>.modern-python.org` (only some repos have one).
+
+## Repository metadata (three surfaces kept consistent)
+
+Every repo's summary appears in up to three places — keep them saying the same thing:
+the **GitHub description**, the pyproject **`description`**, and the repo's blurb in
+`profile/README.md`. Write one canonical one-liner per repo: purpose-first,
+≤ ~120 chars, **no trailing period** (GitHub convention).
+
+### GitHub topics
+- Lowercase letters/numbers/hyphens only, ≤50 chars each, ≤12 per repo.
+- Draw from the shared org vocabulary so `/topics/*` pages cluster: `python`,
+  `dependency-injection`, `di`, `ioc-container`, `modern-di`, `fastapi`, `litestar`,
+  `faststream`, `sqlalchemy`, `postgresql`, `asyncio`, `docker`, `cli`, `messaging`.
+- `modern-di-*` integrations share a base set
+  (`python, dependency-injection, di, ioc-container, modern-di`) plus their framework.
+- Also set the repo **website field** to its docs site, or `modern-python.org` if none.
+
+### pyproject `[project]`
+- **`keywords`** mirror the GitHub topics (lowercase/hyphenated). Never use
+  `"dependency injector"` — that is another package's name (`dependency-injector`).
+- **`classifiers`**: include `Development Status :: <level>`,
+  `Intended Audience :: Developers`, the relevant `Programming Language :: Python ::`
+  versions, `Typing :: Typed`, and a `Topic ::` where apt. Validate every string
+  against <https://pypi.org/classifiers/> before committing.
+- **Do NOT add a `License :: OSI Approved :: ...` classifier.** All repos are MIT and
+  declare the SPDX `license = "MIT"` key; PEP 639 deprecates pairing that with a
+  License classifier, and `uv_build` warns on it.
+- **`[project.urls]`** uses PyPI well-known labels (capitalized):
+  `Homepage`, `Documentation` (only if a docs site exists), `Repository`,
+  `Issues` (`…/issues`), `Changelog` (`…/releases`).
+
+## Tooling
+
+Projects use **uv** (packaging), **ruff** (lint/format), **ty** (type check), and
+the build backend is **uv_build**. `that-depends` additionally runs `mypy` and
+`pyrefly` in its `lint-ci` recipe. Lint/test live behind a `justfile` in most repos.
+
+## CI gotcha
+
+GitHub occasionally type-checks a **stale `refs/pull/<n>/merge`** after a push, so a
+PR can show an old lint/test failure that no longer matches the branch. Confirm by
+running the failing check locally at the branch HEAD (with the pinned tool version);
+if it's clean, push a fresh commit to force GitHub to recompute the merge ref.