refactor(person-mention): hoist LoadState + HoverData into shared types module

Markus flagged the LoadState export from PersonHoverCard.svelte as a
view-vs-orchestrator boundary smell — both files own the same shape, and a
third caller (admin previews, briefwechsel cards) would create a circular
import. Move the types into src/lib/types/personHoverCard.ts so the contract
is module-stable.

Also harden .prettierignore + eslint.config.js so a stray .svelte-kit.old/
backup directory (rotated by SvelteKit during dev) doesn't break the lint
hook — matches the existing .svelte-kit-backup/ convention.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/eslint.config.js

@@ -12,7 +12,7 @@ const gitignorePath = fileURLToPath(new URL('./.gitignore', import.meta.url));
 
 export default defineConfig(
 	includeIgnoreFile(gitignorePath),
-	{ ignores: ['src/paraglide/**'] },
+	{ ignores: ['src/paraglide/**', '.svelte-kit.old/**'] },
 	js.configs.recommended,
 	...ts.configs.recommended,
 	...svelte.configs.recommended,