docs: add disk capacity incident runbook (Closes #1287)

tests/test_ops_fundamentals.py

@@ -0,0 +1,16 @@
+from pathlib import Path
+
+
+RUNBOOK = Path(__file__).parents[1] / "docs" / "ops-fundamentals.md"
+
+
+def test_disk_capacity_runbook_requires_safe_remediation_and_release_verification():
+    text = " ".join(RUNBOOK.read_text().split())
+
+    assert "Disk capacity incident" in text
+    assert "85%" in text
+    assert "df -h / /var/lib/gitea" in text
+    assert "disposable caches and abandoned temporary environments" in text
+    assert "must not delete Gitea data" in text
+    assert "systemctl is-active gitea act_runner" in text
+    assert "repository test suite" in text