Move texts to Paraglide JS; Rust reads the same message files

[firsttris]

This moves prefixr's texts to Paraglide JS, as already done in quadeck and haul. They move from src/lib/i18n/{de,en}.ts to messages/{de,en}.json and are compiled into typed message functions. Rust now reads the same two files, so every text exists only once.

Changes

• Frontend
  • t("gameForm.tabCount", { count }) becomes m.gameForm_tabCount({ count }). This covers all 419 texts, and the placeholders keep their names.
  • Ids chosen at runtime go through pickMsg(msgGroup.x, id): wine tools, Proton options, winetricks verbs, MangoHud presets and colours.
  • The language is still a $state, and Paraglide reads it on every call, so switching re-renders every text without a reload. I checked this in the browser: after a click on "EN", the navigation and content were English straight away.
• Backend errors stay structured: AppError is sent as { code, ...fields }, and the frontend shows backendErrors_<code> with the fields as placeholders.
• Rust's own texts now come from messages/*.json, built into the binary (locale::text). That covers:
  • the tray menu and the quit dialog;
  • the dialogs for running as root and for an unreadable config;
  • the headless launch failure dialog;
  • AppError::localized(), so the second copy of every backend error text in error.rs is gone.
• Dependencies: @inlang/paraglide-js, @inlang/plugin-message-format, vitest, and @types/node, which Paraglide's generated files need for svelte-check. With @types/node in place, the @ts-expect-error in vite.config.js was no longer needed and is removed.
• README: new section "Texts and languages".

Tests

• vitest (bun run test, new CI step), in tests/i18n.test.ts:
  • both languages have the same keys and placeholders, and no text is empty;
  • every message is used, by the UI or by Rust;
  • every used key exists.
• cargo test:
  • every AppError variant has its backendErrors_<code> message, with the variant's fields as placeholders;
  • every key Rust renders exists;
  • AppError::localized and locale::text render correctly.
  • The existing tray tests still pass unchanged, so the texts read from JSON are identical to the old ones.

Checks run:

• bun install --frozen-lockfile ✅
• bun run check: 0 errors ✅
• bun run test ✅
• cargo test --locked: 129 passed ✅
• bun run build ✅

🤖 Generated with Claude Code

https://claude.ai/code/session_014W49icb7XZqhYXUBc1UjzL

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Generated by Claude Code