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);
+}