Consolidate all study-dependent routes and UI

- Remove global experiments and plugins routes; redirect to study-scoped
  pages
- Update sidebar navigation to separate platform-level and study-level
  items
- Add study filter to dashboard and stats queries
- Refactor participants, trials, analytics pages to use new header and
  breadcrumbs
- Update documentation for new route architecture and migration guide
- Remove duplicate experiment creation route
- Upgrade Next.js to 15.5.4 in package.json and bun.lock

src/app/(dashboard)/studies/[id]/participants/page.tsx

@@ -2,8 +2,11 @@
 
 import { useParams } from "next/navigation";
 import { Suspense, useEffect } from "react";
+import { Users, Plus } from "lucide-react";
 import { ParticipantsTable } from "~/components/participants/ParticipantsTable";
-import { ManagementPageLayout } from "~/components/ui/page-layout";
+import { PageHeader } from "~/components/ui/page-header";
+import { Button } from "~/components/ui/button";
+import { useBreadcrumbsEffect } from "~/components/ui/breadcrumb-provider";
 import { useStudyContext } from "~/lib/study-context";
 import { useSelectedStudyDetails } from "~/hooks/useSelectedStudyDetails";
 
@@ -13,6 +16,14 @@ export default function StudyParticipantsPage() {
   const { setSelectedStudyId, selectedStudyId } = useStudyContext();
   const { study } = useSelectedStudyDetails();
 
+  // Set breadcrumbs
+  useBreadcrumbsEffect([
+    { label: "Dashboard", href: "/dashboard" },
+    { label: "Studies", href: "/studies" },
+    { label: study?.name ?? "Study", href: `/studies/${studyId}` },
+    { label: "Participants" },
+  ]);
+
   // Sync selected study (unified study-context)
   useEffect(() => {
     if (studyId && selectedStudyId !== studyId) {
@@ -21,23 +32,24 @@ export default function StudyParticipantsPage() {
   }, [studyId, selectedStudyId, setSelectedStudyId]);
 
   return (
-    <ManagementPageLayout
-      title="Participants"
-      description="Manage participant registration, consent, and trial assignments for this study"
-      breadcrumb={[
-        { label: "Dashboard", href: "/dashboard" },
-        { label: "Studies", href: "/studies" },
-        { label: study?.name ?? "Study", href: `/studies/${studyId}` },
-        { label: "Participants" },
-      ]}
-      createButton={{
-        label: "Add Participant",
-        href: `/studies/${studyId}/participants/new`,
-      }}
-    >
+    <div className="space-y-6">
+      <PageHeader
+        title="Participants"
+        description="Manage participant registration, consent, and trial assignments for this study"
+        icon={Users}
+        actions={
+          <Button asChild>
+            <a href={`/studies/${studyId}/participants/new`}>
+              <Plus className="mr-2 h-4 w-4" />
+              Add Participant
+            </a>
+          </Button>
+        }
+      />
+
       <Suspense fallback={<div>Loading participants...</div>}>
         <ParticipantsTable studyId={studyId} />
       </Suspense>
-    </ManagementPageLayout>
+    </div>
   );
 }