- Add alwaysOpen prop to DevTools.svelte so the iframe path starts open
  (standalone badge/close mode is unaffected)
- Pass alwaysOpen={true} from iframe-entry.ts
- Extract all overlay CSS to devtools.css as single source of truth;
  main.ts imports it via ?raw for shadow DOM injection, index.html
  links it directly — no more duplicate/drifting style blocks
- Add high-specificity iframe overrides in index.html so the panel
  fills the DevTools window instead of rendering at 440x580px fixed
- Add full tb-btn / titlebar-left / paused-banner rules that were
  missing from the iframe stylesheet
- Fix plugin paths and dynamic @vitejs/devtools-kit import
- Add preserveEntrySignatures and external deps to vite.config.ts