Optimize OpenUI Cloud Lighthouse performance

[zahlekhan]

Summary

• reduce the OpenUI Cloud page transfer size with responsive WebP assets and losslessly optimized SVGs
• replace heavyweight client-side Cloud hero/feature rendering with server-rendered and native image behavior
• split route-specific UI, chart, and agent surface bundles so they are not loaded by /cloud
• defer PostHog and Google Analytics work until after the first paint/idle window
• remove first-interaction animation, observer, and count-up work from shared marketing components
• fix Cloud page landmarks, contrast, accessible labels, and theme image behavior

Why

The /cloud route was loading large shared UI/chart/agent bundles, both theme variants of heavy artwork, and analytics/observer work on the main thread. That kept the thread busy around the first pointer interaction and produced the reported 576 ms INP event.

Impact

Mobile Lighthouse production-mode comparison:

Metric	Live baseline	Optimized local build
Performance	40	90
Accessibility	91	100
Best Practices	100	100
SEO	100	100
LCP	18.6 s	3.6 s
Total Blocking Time	830 ms	10 ms
Max potential input delay	660 ms	70 ms
Transfer size	3.9 MB	514 KiB

Validation

• pnpm --dir docs exec tsc --noEmit --pretty false
• scoped ESLint for the Cloud route, shared header/theme controls, and rebased layouts
• git diff upstream/main...HEAD --check
• browser QA for desktop rendering and light/dark asset switching
• Lighthouse: 90 Performance, 100 Accessibility, 100 Best Practices, 100 SEO, 100 Agentic Browsing

The repository-wide lint command still reports existing errors and warnings in unrelated demo/import pages; the Cloud scope included here is clean.

[zahlekhan]

Superseded by four focused draft PRs:

• Optimize OpenUI Cloud media delivery and rendering #880 — Cloud media delivery and rendering
• Isolate docs bundles and route-specific styles #881 — bundle boundaries and route-specific styles
• Defer site analytics initialization #882 — deferred analytics initialization
• Reduce marketing interaction main-thread work #883 — marketing interaction main-thread cleanup

Each replacement is independently based on current main, type-checked, and mergeable. The original cumulative Lighthouse results and discussion remain available in this PR for reference.