feat(scenarios): add step title, scenario credentials, and environment context in executor

- add nullable title column to scenario steps; exposed in create/edit forms and step table
- add scenario-credential join (many-to-many with CredentialEntity) with CRUD endpoints
- expose environment URLs in code executor helpers via helpers.env and helpers.getEnvUrl()
- resolve and cache environment per run from the login step's environmentName in scheduler
- add section spacing and step table title column to ScenarioDetailPage

client/src/pages/scenario/EditStepPage.tsx

@@ -16,6 +16,7 @@ export function EditStepPage() {
   const [scenario, setScenario] = useState<Scenario | null>(null);
   const [step, setStep] = useState<ScenarioStep | null>(null);
   const [order, setOrder] = useState('');
+  const [title, setTitle] = useState('');
   const [type, setType] = useState<StepType>('exec');
   const [sessionName, setSessionName] = useState('');
   const [execCode, setExecCode] = useState('');
@@ -33,6 +34,7 @@ export function EditStepPage() {
         setScenario(sc);
         setStep(st);
         setOrder(String(st.order));
+        setTitle(st.title ?? '');
         setType(st.type);
         setSessionName(st.sessionName);
         setExecCode(st.execCode ?? '');
@@ -63,6 +65,7 @@ export function EditStepPage() {
     try {
       await steps.update(Number(id), Number(stepId), {
         order: Number(order),
+        title: title.trim() || undefined,
         type,
         sessionName: sessionName.trim(),
         execCode: execCode.trim() || undefined,
@@ -109,6 +112,12 @@ export function EditStepPage() {
                 }}
                 error={orderError || undefined}
               />
+              <Input
+                label={t('steps.form_title')}
+                placeholder={t('steps.form_title_placeholder')}
+                value={title}
+                onChange={(e) => setTitle(e.target.value)}
+              />
               <Select
                 label={t('steps.form_type')}
                 value={type}