refactor(web): organize devtools components

[tomerqodo]

Benchmark PR from qodo-benchmark#449

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Note

Consolidates and defers devtools loading to development with dedicated loader components.

• Add ReactScanLoader and TanStackDevtoolsLoader that lazy-load underlying devtools wrapped in Suspense, guarded by IS_DEV (React Scan loader logs and safely no-ops on load failure)
• Replace direct devtools usage: layout.tsx now uses ReactScanLoader; query-client.tsx uses TanStackDevtoolsLoader instead of in-file lazy/Suspense
• Keep existing devtools UIs in devtools/tanstack/devtools.tsx and devtools/react-scan/scan.tsx; no functional app logic changes outside dev-only tooling

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