Admin: compressed assets, deferred trackers, lazy auth, trimmed entry chunk

A full performance pass on the admin app:

• Asset compression at build time on static files.
• Third-party trackers deferred to first interaction instead of loading on first paint.
• The auth SDK is now lazy-loaded out of the entry chunk so visitors who never reach the sign-in form do not pay for it.
• Entry chunk trimmed by removing modules that should have been route-split all along.

LCP on the dashboard dropped by roughly 500-700ms in our continuous Lighthouse run. Most noticeable on the cold first visit.