Unify Install detection and primary actions

[cauyxy]

Summary

• replace the all-false Install bootstrap seed with explicit initial detection, blocking failure, and retained refresh states
• derive exactly one choose/install/repair/launch primary action from completed path, version, and compatibility facts
• extend the semantic problem contract across Install commands and localize warnings and recovery copy in the frontend
• remove the startup event/refetch race and refresh current truth documentation

Testing

• npm run verify -- --source-only
• focused Install Vitest coverage (included in the full 189-test Vitest run)
• Rust semantic contract and Install service tests (183 unit tests plus 3 integration tests)
• Browser Preview in Chinese and English at http://127.0.0.1:14207/: explicit detection state, exactly one primary action, localized warnings, no console errors, no overflow
• macOS npm run tauri dev smoke: native startup and first Install detection resolved the local Steam/The Bazaar installation successfully
• Native UI automation could not attach to the unbundled Tauri dev window; no destructive install/reset/uninstall/launch action was exercised against the real game data

Closes #25

Release Notes:

• 安装页现在会先完成真实检测，再提供唯一且一致的主操作，并用本地化提示保留失败前的有效状态。