docs(readme): polish launch highlights and banner (#261)

* docs: simplify README launch highlights

* docs(readme): use six launch highlights

* docs(readme): use optimized banner asset

* ci: lint pull request titles

tests/unit/test_scripts/test_check_pr_title.py

@@ -0,0 +1,56 @@
+"""Self-tests for ``scripts/check_pr_title.py``."""
+
+from __future__ import annotations
+
+import importlib.util
+import sys
+from pathlib import Path
+
+_REPO_ROOT = Path(__file__).resolve().parents[3]
+_CHECKER_PATH = _REPO_ROOT / "scripts" / "check_pr_title.py"
+
+
+def _load_checker():
+    assert _CHECKER_PATH.exists(), "PR title checker should exist"
+    spec = importlib.util.spec_from_file_location("_pr_title_checker", _CHECKER_PATH)
+    assert spec and spec.loader
+    mod = importlib.util.module_from_spec(spec)
+    sys.modules[spec.name] = mod
+    spec.loader.exec_module(mod)
+    return mod
+
+
+def test_conventional_pr_title_is_allowed() -> None:
+    checker = _load_checker()
+
+    assert checker.validate_title("docs(readme): polish launch highlights") == []
+
+
+def test_bracketed_codex_pr_title_is_blocked() -> None:
+    checker = _load_checker()
+
+    failures = checker.validate_title("[codex] simplify README launch highlights")
+
+    assert len(failures) == 1
+    assert "invalid PR title" in failures[0]
+    assert "expected: <type>[(scope)][!]: <description>" in failures[0]
+
+
+def test_long_pr_title_is_blocked() -> None:
+    checker = _load_checker()
+    title = (
+        "docs(readme): polish launch highlights and banner with a title that is "
+        "too long"
+    )
+
+    failures = checker.validate_title(title)
+
+    assert len(failures) == 1
+    assert "max is 72" in failures[0]
+
+
+def test_main_reads_pr_title_environment(monkeypatch) -> None:
+    checker = _load_checker()
+    monkeypatch.setenv("PR_TITLE", "docs(readme): polish launch highlights")
+
+    assert checker.main([]) == 0