[codex] Lazy load feature modules

[panghim]

Summary

• lazy-load major feature modules from App.tsx with React.lazy and Suspense
• add a lightweight module loading placeholder
• update the collaboration queue and maintenance log for the 2026-06-16 maintenance pass

Impact

This keeps the app shell smaller and turns feature screens into async chunks. It directly addresses the current bundle-size/code-splitting maintenance track.

Evidence

Before this change, npm run build produced one entry chunk:

• dist/assets/index-CjRptPdA.js: 1,242.11 kB / gzip 322.44 kB
• Vite emitted the Some chunks are larger than 500 kB warning

After this change, npm run check produced:

• dist/assets/index-vB2h1zPc.js: 220.24 kB / gzip 70.02 kB
• feature-specific async chunks for Dashboard, InvoiceManager, TaxDeclaration, CrossBorderHub, OpenPlatform and other modules
• no Vite chunk-size warning
• 25 Vitest tests passed

Checks

• npm run check

Closes #26.
Related #29.