feat(editor): add TypeScript script tooling

[DavidBabinec]

Summary

• add lazy, worker-isolated TypeScript language tooling to Site Editor scripts
• provide strict semantic diagnostics, DOM-aware completions and hover information, plus relative cross-file typing
• merge semantic diagnostics into a compact, scrollable and minimizable Problems panel
• preserve explicit TypeScript script extensions and keep autocomplete/hover popups inside the editor boundary
• render TypeScript hover documentation as safe Markdown

Why

Site script authors currently get syntax highlighting and publish-time compilation, but not the semantic editing feedback expected from TypeScript tooling. This addresses the workflow requested in Discussion #351 while keeping esbuild as the authoritative canvas and publish compiler.

User impact

Authors receive type errors, DOM API suggestions, signatures, and cross-file type information directly in the Code tab. The language service loads only when a TypeScript script is opened and runs off the UI thread. Large diagnostic sets remain bounded and can collapse to their error count.

Verification

• bun test ./src/__tests__/admin/siteItemNames.test.ts ./src/__tests__/architecture/typescript-language-worker-isolation.test.ts ./src/__tests__/architecture/bundle-size-budgets.test.ts ./src/__tests__/code-editor/codeMirrorEditor.test.tsx ./src/__tests__/code-editor/scriptSettingsPane.test.tsx ./src/__tests__/code-editor/typescriptLanguageService.test.ts
• bun run lint
• bun run build
• git diff --check
• live disposable browser pass covering diagnostics, completion, hover, autosave/reload, publish/runtime execution, Problems minimization, and right-edge autocomplete containment