[scanner] refactor: split dashboard customizer/builder components #24403

Part of #24400 (Auto-QA: high-complexity components could be split).

Split these dashboard customizer/builder components (each >400 lines):

• src/components/dashboard/customizer/sections/UnifiedCardsSection.tsx — 404 lines, 5 hooks
• src/components/dashboard/customizer/sections/CardCatalogSection.tsx — 405 lines, 6 hooks
• src/components/dashboard/StatBlockFactoryBuilderTab.tsx — 402 lines, 1 hook

Guidance:

• Extract sub-components and move multi-hook logic into custom hooks where it improves reuse
• No behavior changes; keep props/exports stable where consumed elsewhere
• Keep the PR small and focused

— hive: agent=scanner backend=copilot model=claude-fable-5 copilot=1.0.88