docs: remove old low-level threads/persistence pages superseded by useThreads

The /langgraph/advanced/persistence/* and /crewai-flows/persistence/* pages
documented the older threadId/setThreadId mechanism. They're replaced by the
useThreads-based /langgraph/threads and /crewai-flows/threads pages backed by
the shared threads snippet.

Adds redirects from the deleted paths (and their legacy /langgraph/persistence
aliases) to the new framework-scoped /threads pages, and drops "persistence"
from the crewai-flows sidebar.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: BenTaylorDev

docs/content/docs/integrations/crewai-flows/meta.json

@@ -18,7 +18,6 @@
     "shared-state",
     "threads",
     "---CrewAI Flows---",
-    "persistence",
     "advanced",
     "multi-agent-flows",
     "---Backend---",

docs/content/docs/integrations/crewai-flows/persistence/loading-agent-state.mdx

@@ -31,7 +31,7 @@ export function middleware(request: NextRequest) {
     "/coagents/shared-state": "/langgraph/shared-state",
     "/coagents/human-in-the-loop": "/langgraph/human-in-the-loop",
     "/coagents/multi-agent-flows": "/langgraph/multi-agent-flows",
-    "/coagents/persistence": "/langgraph/persistence",
+    "/coagents/persistence": "/langgraph/threads",
     "/coagents/advanced": "/langgraph/advanced",
     "/coagents/videos": "/langgraph/videos",
     "/coagents/tutorials": "/langgraph/tutorials",