feat(shared): use web components for search, select, and checkbox controls - #352

Summary

• Add shared pptx-ui-search, pptx-ui-select, and pptx-ui-checkbox custom elements. They use the existing --pptx-* theme tokens and provide one event and keyboard interaction contract across bindings.
• Keep scoped styles in readable modules. Browser instances share a parsed stylesheet per document and control type, with a <style> fallback for DOMs without constructable stylesheet support.
• Migrate the title-bar and File recent search fields, File > Options controls, and select and checkbox controls in the Properties inspector for React, Vue, Angular, Svelte, and Vanilla. The select popup opens below its trigger and retains the existing dark UI treatment.
• Keep the File navigation implementation unchanged. Other native controls remain available for later migration batches.

Verification

• Full package test suites: shared 9,960 passed; React 7,390; Vue 3,056; Angular 3,840; Svelte 1,930; Vanilla 1,967.
• Browser tests across all five bindings: 15 search focus, forced-colors, and narrow viewport checks; 10 Properties interaction and stylesheet reuse checks.
• Type checks for all five bindings and shared, Angular package build, formatting, lint, and the E2E framework-neutrality check passed.

Closes #348
Closes #349
Related to #342