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/ui/Textarea/Textarea.module.css

@@ -0,0 +1,60 @@
+.wrapper {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-1);
+  font-family: var(--font-family);
+  width: 100%;
+}
+
+.label {
+  font-size: var(--font-size-sm);
+  font-weight: 500;
+  color: var(--color-text);
+}
+
+.textarea {
+  font-family: var(--font-family-mono, monospace);
+  font-size: var(--font-size-sm);
+  color: var(--color-text);
+  background: var(--color-bg);
+  border: var(--border-width) solid var(--color-border);
+  border-radius: var(--radius-md);
+  padding: var(--space-2) var(--space-3);
+  width: 100%;
+  outline: none;
+  resize: vertical;
+  transition: border-color var(--transition), box-shadow var(--transition);
+}
+
+.textarea::placeholder {
+  color: var(--color-text-muted);
+}
+
+.textarea:focus {
+  border-color: var(--color-primary);
+  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.2);
+}
+
+.textarea:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+  background: var(--color-bg-subtle);
+}
+
+.hasError {
+  border-color: var(--color-error-fg);
+}
+.hasError:focus {
+  border-color: var(--color-error-fg);
+  box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.2);
+}
+
+.hint {
+  font-size: var(--font-size-xs);
+  color: var(--color-text-muted);
+}
+
+.error {
+  font-size: var(--font-size-xs);
+  color: var(--color-error-fg);
+}

client/src/ui/Textarea/Textarea.tsx

@@ -0,0 +1,40 @@
+import React, { useId } from 'react';
+import styles from './Textarea.module.css';
+
+export interface TextareaProps
+  extends Omit<React.TextareaHTMLAttributes<HTMLTextAreaElement>, 'id'> {
+  label?: string;
+  hint?: string;
+  error?: string;
+}
+
+export function Textarea({ label, hint, error, className, ...props }: TextareaProps) {
+  const id = useId();
+  return (
+    <div className={styles.wrapper}>
+      {label && (
+        <label htmlFor={id} className={styles.label}>
+          {label}
+        </label>
+      )}
+      <textarea
+        id={id}
+        className={[styles.textarea, error ? styles.hasError : '', className]
+          .filter(Boolean)
+          .join(' ')}
+        aria-describedby={error ? `${id}-error` : hint ? `${id}-hint` : undefined}
+        aria-invalid={error ? true : undefined}
+        {...props}
+      />
+      {error ? (
+        <span id={`${id}-error`} className={styles.error} role="alert">
+          {error}
+        </span>
+      ) : hint ? (
+        <span id={`${id}-hint`} className={styles.hint}>
+          {hint}
+        </span>
+      ) : null}
+    </div>
+  );
+}