chore: add Justfile and .markdownlint.jsonc, update README

.markdownlint.jsonc

@@ -0,0 +1,27 @@
+// Project-wide markdownlint configuration.
+// Docs: https://github.com/DavidAnson/markdownlint/blob/main/doc/Rules.md
+{
+  "default": true,
+
+  // Line length: disabled. CHANGELOG entries, badge URLs and inline code
+  // references frequently exceed 80 columns; soft-wrap is handled by the
+  // renderer, not by hard line breaks in source.
+  "MD013": false,
+
+  // Duplicate headings: permitted across sibling scopes. Keep a Changelog
+  // mandates repeated `### Added` / `### Changed` / `### Removed` under each
+  // version, but we still flag accidental duplicates within the same scope.
+  "MD024": { "siblings_only": true },
+
+  // Inline HTML: permitted. README uses <p align="center">, <img>, <a> and
+  // similar elements for badges, centered headers and tables.
+  "MD033": false,
+
+  // Emphasis used as heading: permitted. Lightweight **bold** section labels
+  // are common in changelogs and migration blocks.
+  "MD036": false,
+
+  // First line must be a top-level heading: disabled. README typically opens
+  // with badges or centered logo blocks before the `# Title` heading.
+  "MD041": false
+}

Justfile

@@ -0,0 +1,40 @@
+# Run all checks and tests.
+all: check test
+
+# Show all available recipes.
+help:
+    @just --list
+
+# Install the package in editable mode with all dependencies.
+install:
+    uv sync --extra dev --extra all
+    uv run pre-commit install
+
+# Run Ruff lint checks.
+lint:
+    uv run ruff check .
+
+# Auto-fix Ruff findings and format the code.
+format:
+    uv run ruff check --fix .
+    uv run ruff format .
+
+# Run the mypy type checker.
+typecheck:
+    uv run mypy src/x402_openai
+
+# Run pytest.
+test:
+    uv run pytest
+
+# Build wheel and source distributions.
+build:
+    uv build
+
+# Remove build artifacts and caches using the project's Python environment.
+clean:
+    uv run python -c "import shutil, pathlib; [shutil.rmtree(p, ignore_errors=True) for p in ['dist', 'build', '.mypy_cache', '.pytest_cache']]; [shutil.rmtree(p) for p in pathlib.Path('.').rglob('__pycache__')]; [shutil.rmtree(p) for p in pathlib.Path('.').rglob('*.egg-info')]"
+
+# Run all pre-commit hooks.
+check:
+    uv run pre-commit run --all-files

README.md

@@ -155,11 +155,10 @@ This project is licensed under the [MIT License](LICENSE).
 
 <div align="center">
 
-A **[QNTX](https://qntx.fun)** open-source project.
+A **[QuantX](https://qntx.fun)** open-source project.
 
-<a href="https://qntx.fun"><img alt="QNTX" width="369" src="https://raw.githubusercontent.com/qntx/.github/main/profile/qntx-banner.svg" /></a>
+<a href="https://qntx.fun"><img alt="QuantX" width="369" src="https://raw.githubusercontent.com/qntx/.github/main/profile/qntx.svg" /></a>
 
-<!--prettier-ignore-->
 Code is law. We write both.
 
 </div>