fix(FN-5257): restore SecretsView action icon visibility

- Standardize SecretsView action icon sizing and color so header, row, loading, and modal toggle icons stay visible in dark and light themes
- Expand SecretsView tests to load app CSS and assert icon visibility across both themes
- Stabilize the process supervisor fallback test by removing an unnecessary maxLifetime override

Fusion-Task-Id: FN-5257

packages/dashboard/app/components/SecretsView.css

@@ -160,13 +160,30 @@
   flex: 1;
 }
 
-.secrets-visibility-toggle {
+.secrets-action-icon {
+  width: 1em;
+  height: 1em;
+  min-width: 1em;
+  min-height: 1em;
+  flex-shrink: 0;
+  display: block;
+  stroke: currentColor;
+  font-size: var(--icon-size-sm);
+}
+
+.secrets-header-actions .btn,
+.secrets-row-actions .btn,
+.secrets-value-row .btn-icon {
   color: var(--text);
 }
 
-.secrets-visibility-toggle > svg {
-  display: block;
-  stroke: currentColor;
+.secrets-header-actions .btn-primary,
+.secrets-row-actions .btn-danger {
+  color: var(--cta-text);
+}
+
+.secrets-row-actions .btn:disabled {
+  color: var(--text-muted);
 }
 
 @media (max-width: 768px) {