Fix SSR and automerge timing

SSR fix:
- ClientOnly wrapper prevents Leaflet/Yjs from running during SSR
- SessionView lazy-loaded to avoid browser API usage on server

Automerge fix:
- Set MERGE_READY_STATE to 'clean' only (was including 'unstable')
- Prevents merging before all CI checks complete

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/planner/app/components/ClientOnly.tsx

@@ -0,0 +1,17 @@
+import { useState, useEffect, type ReactNode } from "react";
+
+export function ClientOnly({
+  children,
+  fallback = null,
+}: {
+  children: () => ReactNode;
+  fallback?: ReactNode;
+}) {
+  const [mounted, setMounted] = useState(false);
+
+  useEffect(() => {
+    setMounted(true);
+  }, []);
+
+  return mounted ? <>{children()}</> : <>{fallback}</>;
+}