perf: faster dev startup and lighter bundle

- Switch dev default to Turbopack (5-14x faster compile); keep webpack as dev:webpack
- Tailwind v4 source() base so JIT scans identically under both bundlers
- Lazy-load @xyflow/react via next/dynamic to keep it out of the shared bundle
- optimizePackageImports for heavy barrel imports (xyflow, dnd-kit, material-symbols, marked)
- Replace blind setTimeout waits with TCP health-check (waitServerReady)
- Run checkForUpdate in parallel instead of blocking server spawn
- Background MITM/tunnel/cloudflared kills off the critical path

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -77,3 +77,4 @@ gitbook/README.md
 open-sse.old/
 .graphifyignore
 graphify-out/*
+.next-analyze/*