feat: port release-v2 experience improvements from PR #6582

Brings the semantically-correct unification work from the closed
agent/release-v2-experience PR into release/v2:

- universal create surface (header, board, spotlight) with permission-aware actions
- board empty state and setup checklist with widget/connection recipes
- in-widget integration editing via inspector modal, preserving unsaved widget settings
- single-source widget-integration capability map (nativeFeatureCapabilities)
- multi-endpoint Docker singleton with per-endpoint failure isolation, DOCKER_ENDPOINTS descriptors and service reconciliation
- Kubernetes multi-context registry with availability probing and context selector
- response-contract test harness and setup analytics property boundaries

Excludes the feature-platform generator/workbench tooling (deferred).

apps/nextjs/src/components/create/universal-create-modal.module.css

@@ -0,0 +1,21 @@
+.action {
+  width: 100%;
+  border-radius: var(--mantine-radius-md);
+  padding: var(--mantine-spacing-sm);
+  text-align: start;
+}
+
+@media (hover: hover) {
+  .action:hover {
+    background: var(--mantine-color-default-hover);
+  }
+}
+
+.action:focus-visible {
+  outline: 2px solid var(--mantine-primary-color-filled);
+  outline-offset: 2px;
+}
+
+.actionIcon {
+  flex: 0 0 auto;
+}