Use the published @voltius/plugin-types instead of vendored types

[kipavy]

The template vendored types/index.d.ts + types/voltius-ui.d.ts and pointed tsconfig.json paths at them, because @voltius/plugin-types did not exist on npm. It does now — 0.15.0 published with the Voltius 0.15.0 release — so the template can use what it tells authors to use.

• @voltius/plugin-types@^0.15.0 becomes a dev dependency
• both vendored .d.ts files are deleted (746 lines)
• tsconfig.json drops baseUrl/paths entirely and narrows include to src
• the README ## Types section now documents npm install --save-dev @voltius/plugin-types and the version-tracks-the-app rule

@voltius/ui still resolves with no paths mapping: the published index.d.ts pulls in ui.d.ts through a /// reference, and that file is byte-identical to the copy being deleted. The vendored index.d.ts differed from the published one by exactly one line — the /// reference itself — so the API surface authors compile against does not change.

Verified from a clean node_modules: npm install, npm run typecheck, npm run build and npm run check all exit 0. check fetches the host specifier list live from voltius main and reports react, @voltius/ui, react/jsx-runtime as the bundle imports, all host-provided.