Update now: download, verify and install a release in one click (#1118)

Where SolidCraft can replace itself safely, the Update window gets Update now:
- AppImage: the new AppImage is downloaded next to the old one, verified and renamed over
  it; Restart now starts it as SolidCraft exits.
- Windows MSI: the verified .msi starts (msiexec /i … /passive) once SolidCraft has closed,
  after the usual questions about unsaved designs.
- Windows portable zip / standalone exe: the running solidcraft.exe is renamed to .old, the
  new one takes its name (solidcraft-cli.exe too), Restart now; .old goes at the next start.
- macOS: the verified .dmg is opened (the app is ad-hoc signed and not notarized, so it isn't
  replaced behind the user's back).
- Flatpak, Snap, deb, rpm, tar.gz: never replaced; the window shows the command.

Every package's SHA-256 must match the release's SHA256SUMS.txt (HTTPS, same release); a
mismatch deletes the download and changes nothing. With PUBLIC_KEY set in update/install.rs,
SHA256SUMS.txt.minisig must also verify (minisign-verify, MIT) with a trusted comment naming
the release. release.yml signs the list when the UPDATE_SIGNING_KEY secret exists and fails
when the app expects signatures but the secret is missing; docs/releasing.md has the steps.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

assets/locales/de.json

@@ -725,5 +725,15 @@
   "update.prefs_note": "Dies ist SolidCraft {version} ({kind}). Die Suche fragt GitHub nach dem neuesten Release und sendet sonst nichts.",
   "update.prefs_dev": "Dies ist ein Entwicklungs-Build ({version}): er sucht nicht nach Updates.",
   "update.show": "Update auf {version} anzeigen",
-  "update.prefs_flatpak": "Flatpak aktualisiert diese Installation ({version}): {command} ausführen oder die Softwareverwaltung nutzen. SolidCraft sucht nicht selbst."
+  "update.prefs_flatpak": "Flatpak aktualisiert diese Installation ({version}): {command} ausführen oder die Softwareverwaltung nutzen. SolidCraft sucht nicht selbst.",
+  "update.update_now": "Jetzt aktualisieren",
+  "update.install_msi": "Installieren (schließt SolidCraft)",
+  "update.download_open": "Herunterladen und öffnen",
+  "update.downloading": "Herunterladen und prüfen… {done} von {total} MB",
+  "update.installed": "SolidCraft {version} ist installiert. Zum Verwenden neu starten.",
+  "update.restart": "Jetzt neu starten",
+  "update.restart_later": "Später",
+  "update.installer_started": "Das Installationsprogramm startet, wenn SolidCraft geschlossen wird.",
+  "update.dmg_opened": "Das Disk-Image ist geöffnet und geprüft: SolidCraft in „Programme“ ziehen, die alte Version ersetzen und SolidCraft neu starten.",
+  "update.install_failed": "Das Update wurde nicht installiert: {error}. Es wurde nichts verändert; „Herunterladen“ holt das Paket."
 }

assets/locales/en.json

@@ -984,5 +984,15 @@
   "update.prefs_note": "This is SolidCraft {version} ({kind}). A check asks GitHub for the latest release and sends nothing else.",
   "update.prefs_dev": "This is a development build ({version}): it doesn't check for updates.",
   "update.show": "Show the update to {version}",
-  "update.prefs_flatpak": "Flatpak updates this copy ({version}): run {command} or use your software center. SolidCraft doesn't check."
+  "update.prefs_flatpak": "Flatpak updates this copy ({version}): run {command} or use your software center. SolidCraft doesn't check.",
+  "update.update_now": "Update now",
+  "update.install_msi": "Install (closes SolidCraft)",
+  "update.download_open": "Download and open",
+  "update.downloading": "Downloading and verifying… {done} of {total} MB",
+  "update.installed": "SolidCraft {version} is installed. Restart to use it.",
+  "update.restart": "Restart now",
+  "update.restart_later": "Later",
+  "update.installer_started": "The installer starts when SolidCraft closes.",
+  "update.dmg_opened": "The disk image is open and verified: drag SolidCraft to Applications, replacing the old copy, then restart SolidCraft.",
+  "update.install_failed": "The update didn't install: {error}. Nothing was changed; Download gets the package instead."
 }

assets/locales/ja.json

@@ -984,5 +984,15 @@
   "update.prefs_note": "これは SolidCraft {version} ({kind}) です。確認では GitHub に最新リリースを問い合わせるだけで、ほかには何も送信しません。",
   "update.prefs_dev": "これは開発ビルド ({version}) のため、アップデートを確認しません。",
   "update.show": "{version} へのアップデートを表示",
-  "update.prefs_flatpak": "このコピー ({version}) は Flatpak が更新します: {command} を実行するか、ソフトウェアセンターを使ってください。SolidCraft 自身は確認しません。"
+  "update.prefs_flatpak": "このコピー ({version}) は Flatpak が更新します: {command} を実行するか、ソフトウェアセンターを使ってください。SolidCraft 自身は確認しません。",
+  "update.update_now": "今すぐ更新",
+  "update.install_msi": "インストール (SolidCraft を終了)",
+  "update.download_open": "ダウンロードして開く",
+  "update.downloading": "ダウンロードと検証中… {done} / {total} MB",
+  "update.installed": "SolidCraft {version} をインストールしました。再起動すると使えます。",
+  "update.restart": "今すぐ再起動",
+  "update.restart_later": "後で",
+  "update.installer_started": "SolidCraft の終了後にインストーラーが起動します。",
+  "update.dmg_opened": "ディスクイメージを検証して開きました: SolidCraft をアプリケーションフォルダにドラッグして古いものを置き換え、SolidCraft を再起動してください。",
+  "update.install_failed": "アップデートをインストールできませんでした: {error}。何も変更されていません。「ダウンロード」でパッケージを入手できます。"
 }

assets/locales/ko.json

@@ -725,5 +725,15 @@
   "update.prefs_note": "SolidCraft {version} ({kind})입니다. 확인 시 GitHub에 최신 릴리스만 요청하며 다른 정보는 보내지 않습니다.",
   "update.prefs_dev": "개발 빌드({version})이므로 업데이트를 확인하지 않습니다.",
   "update.show": "{version} 업데이트 보기",
-  "update.prefs_flatpak": "이 사본({version})은 Flatpak이 업데이트합니다: {command}를 실행하거나 소프트웨어 센터를 사용하세요. SolidCraft는 직접 확인하지 않습니다."
+  "update.prefs_flatpak": "이 사본({version})은 Flatpak이 업데이트합니다: {command}를 실행하거나 소프트웨어 센터를 사용하세요. SolidCraft는 직접 확인하지 않습니다.",
+  "update.update_now": "지금 업데이트",
+  "update.install_msi": "설치 (SolidCraft 종료)",
+  "update.download_open": "다운로드 후 열기",
+  "update.downloading": "다운로드 및 확인 중… {done} / {total} MB",
+  "update.installed": "SolidCraft {version}이(가) 설치되었습니다. 다시 시작하면 사용할 수 있습니다.",
+  "update.restart": "지금 다시 시작",
+  "update.restart_later": "나중에",
+  "update.installer_started": "SolidCraft가 종료되면 설치 프로그램이 시작됩니다.",
+  "update.dmg_opened": "디스크 이미지를 확인하고 열었습니다: SolidCraft를 응용 프로그램 폴더로 끌어 기존 버전을 바꾼 뒤 SolidCraft를 다시 시작하세요.",
+  "update.install_failed": "업데이트를 설치하지 못했습니다: {error}. 아무것도 변경되지 않았습니다. 다운로드로 패키지를 받을 수 있습니다."
 }

assets/locales/zh.json

@@ -984,5 +984,15 @@
   "update.prefs_note": "当前为 SolidCraft {version}({kind})。检查时只向 GitHub 查询最新版本,不发送其他任何数据。",
   "update.prefs_dev": "这是开发版本({version}),不检查更新。",
   "update.show": "显示 {version} 更新",
-  "update.prefs_flatpak": "此副本({version})由 Flatpak 更新:运行 {command} 或使用软件中心。SolidCraft 不会自行检查。"
+  "update.prefs_flatpak": "此副本({version})由 Flatpak 更新:运行 {command} 或使用软件中心。SolidCraft 不会自行检查。",
+  "update.update_now": "立即更新",
+  "update.install_msi": "安装(将关闭 SolidCraft)",
+  "update.download_open": "下载并打开",
+  "update.downloading": "正在下载并校验… {done} / {total} MB",
+  "update.installed": "SolidCraft {version} 已安装。重新启动后生效。",
+  "update.restart": "立即重启",
+  "update.restart_later": "稍后",
+  "update.installer_started": "SolidCraft 关闭后将启动安装程序。",
+  "update.dmg_opened": "磁盘映像已校验并打开:将 SolidCraft 拖到“应用程序”替换旧版本,然后重启 SolidCraft。",
+  "update.install_failed": "更新未安装:{error}。未做任何更改;可用“下载”获取安装包。"
 }