perf: lazy-load panel CSS by moving imports to component files

[sauravpanda]

Summary

• Moved 62 panel-specific CSS imports from src/main.tsx into their respective component files so they are code-split and lazy-loaded
• Kept 6 global/always-visible CSS imports in main.tsx: styles.css, sidebar.css, terminal.css, command-palette.css (multi-component), dashboard.css (multi-component), status-bar.css, project-tabs.css
• 22 components that didn't yet have their CSS import got one added; the remaining already imported their own CSS and just had duplicates removed from main.tsx

Test plan

• pnpm build passes -- CSS files are now emitted as separate per-component chunks
• Verify panels render correctly when opened (styles load on demand)

Closes #305