Performance: code-split markdown renderer, lazy-load on first interaction, Lighthouse CI gate

[PAMulligan]

Summary

Keep the host page fast by lazy-loading the chat panel and its heavy dependencies (markdown renderer, syntax highlighter) only when the user actually opens the widget. Lock in the win with a Lighthouse CI gate.

Motivation

The bubble itself should add near-zero overhead to the host page's TTI/LCP. The current bundle includes the markdown stack up-front; deferring it would meaningfully improve Lighthouse scores for sites embedding Claudius.

Acceptance Criteria

• Initial bundle contains only the floating bubble + open trigger; the chat panel is dynamically imported on first open
• Markdown renderer and any code-highlight bundle code-split out of the initial chunk
• Prefetch on mouseenter of the bubble to mask the latency on intentional opens
• Lighthouse CI runs on every PR against the playground site; fails if Performance score drops below 90
• Bundle-size budget (issue: size-limit) updated to reflect the new initial chunk