chore: add consistent mise.toml, justfile, and tooling config

justfile

@@ -13,3 +13,18 @@ run *args: _ensure_tools
 # Run with verbose logging
 verbose *args: _ensure_tools
     @uv run -m donglora_mux --verbose {{args}}
+
+# Run all checks (fmt, lint)
+check: fmt-check lint
+
+# Format code
+fmt: _ensure_tools
+    @uv run ruff format .
+
+# Check formatting without changing files
+fmt-check: _ensure_tools
+    @uv run ruff format --check .
+
+# Lint
+lint: _ensure_tools
+    @uv run ruff check .

pyproject.toml

@@ -14,6 +14,9 @@ dependencies = [
 [project.scripts]
 donglora-mux = "donglora_mux:main"
 
+[dependency-groups]
+dev = ["ruff"]
+
 [build-system]
 requires = ["hatchling"]
 build-backend = "hatchling.build"