Add engine update button to auto-translate window

[niksedk]

Summary

The auto-translate engine combo shows an amber "update available" status dot for SE-managed engines (CrispASR/MADLAD and llama.cpp) when the installed binary is outdated — but there was previously no way to act on it. CrispASR had no engine-update path at all (DownloadAsync only fetched the binary when it was missing), and llama.cpp only offered a one-time Yes/No prompt when the engine was selected.

This adds an "Update" button right after the engine combobox that appears only when the selected engine is installed but outdated, and re-downloads the engine binary.

Changes

• CrispAsrTranslateDownloadHelper — IsEngineUpdateAvailable() (mirrors the amber dot via DownloadHashManager.GetSidecarStatus) and UpdateEngineAsync() which force-redownloads just the engine binary, leaving MADLAD models untouched.
• AutoTranslateViewModel — generalized UpdateEngine command + RefreshEngineUpdateButton() covering both engines; extracted GetLlamaCppEngineUpdate() / UpdateLlamaCppEngineAsync() so the new button and the existing llama.cpp on-select prompt share a single code path (no behavior change to that prompt).
• AutoTranslateWindow — "Update" button (download icon, "Update available" tooltip) bound to EngineUpdateButtonIsVisible, placed after the engine combobox.

The button stays hidden for cloud/API translators (Google, DeepL, ChatGPT, …) and for engines that are not installed.

Verification

• Builds clean (0 warnings/errors).
• Ran the app and opened the auto-translate window: with CrispASR/MADLAD installed and up to date (green dot), the Update button is correctly hidden — confirming the visibility gating. The amber/button-visible path was confirmed manually.

Uses existing translated strings General.Update / General.UpdateAvailable — no new language keys.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds an "Update" button next to the auto-translate engine combobox that re-downloads the engine binary when an update is available for SE-managed engines (CrispASR/MADLAD, llama.cpp). The button mirrors the amber status dot already shown in the combo and is hidden for cloud/API translators or up-to-date engines.

Changes:

• New CrispAsrTranslateDownloadHelper.IsEngineUpdateAvailable() and UpdateEngineAsync() (CrispASR engine-only force redownload, models untouched).
• AutoTranslateViewModel: new UpdateEngine command, EngineUpdateButtonIsVisible flag and RefreshEngineUpdateButton(); refactored llama.cpp update path into shared GetLlamaCppEngineUpdate() / UpdateLlamaCppEngineAsync() used by both the new button and the existing on-select prompt.
• AutoTranslateWindow: new "Update" button (download icon, "Update available" tooltip) bound to EngineUpdateButtonIsVisible, placed after the engine combo.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/ui/Features/Translate/CrispAsrTranslateDownloadHelper.cs	Adds engine-update detection and engine-only force-redownload helpers for CrispASR/MADLAD.
src/ui/Features/Translate/AutoTranslateViewModel.cs	Adds shared update command, visibility flag and refresh helper; extracts shared llama.cpp update logic.
src/ui/Features/Translate/AutoTranslateWindow.cs	Adds "Update" button bound to the new visibility flag, placed after the engine combobox.