feat(workflow): persist view tab state to URL search params

Use nuqs to sync graph/skill view selection to URL, enabling
shareable links and browser history navigation. Hoists
SkillEditorProvider to maintain state across view switches.

web/app/components/workflow-app/search-params.ts

@@ -0,0 +1,11 @@
+import { parseAsStringEnum } from 'nuqs'
+import { ViewType } from '@/app/components/workflow/types'
+
+export const parseAsViewType = parseAsStringEnum<ViewType>(Object.values(ViewType))
+  .withDefault(ViewType.graph)
+  .withOptions({
+    history: 'replace',
+    clearOnDefault: true,
+  })
+
+export const WORKFLOW_VIEW_PARAM_KEY = 'view'