refactor: remove Tauri auto-updater, replace with simple GitHub-check modal

Remove tauri-plugin-updater, relaunch_after_update command, generate-update-
manifest.js, the generate-manifest CI job, and all signing/upload steps for
.sig files and latest.json. The updater plugin, its pubkey and endpoint config
in tauri.conf.json, and the updater:default capability are all gone.

Replace AppUpdater.tsx with a lightweight component that:
- Fetches https://api.github.com/repos/Psychotoxical/psysonic/releases/latest
  after a 4 s delay (no install, no download, no progress bar)
- Shows a dismissible toast with two buttons:
  GitHub → releases/latest
  Website → https://psysonic.psychotoxic.eu/#downloads

i18n: remove updaterInstall/Downloading/Installing/Download/ExperimentalHint
keys from all 7 locales; add updaterWebsite; update updaterVersion wording.

CI: remove generate-manifest job and all .sig signing/upload steps from
build-macos-windows. Also remove TAURI_SIGNING_PRIVATE_KEY env vars (no
longer needed). Release now just builds and uploads the installable binaries.

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

.github/workflows/release.yml

@@ -80,9 +80,6 @@ jobs:
     needs: create-release
     permissions:
       contents: write
-    env:
-      TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
-      TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
     strategy:
       fail-fast: false
       matrix:
@@ -124,42 +121,6 @@ jobs:
         with:
           releaseId: ${{ needs.create-release.outputs.release_id }}
           args: ${{ matrix.settings.args }}
-          # Prevent tauri-action from auto-uploading a latest.json that uses
-          # the PUBLIC KEY as the signature value. Our generate-update-manifest.js
-          # builds the correct manifest with real .sig file contents.
-          updaterJsonKeepUniversal: false
-
-      - name: sign and upload Windows NSIS updater bundle
-        if: matrix.settings.platform == 'windows-latest'
-        shell: pwsh
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          VERSION: ${{ needs.create-release.outputs.package_version }}
-        run: |
-          $dir = "src-tauri/target/release/bundle/nsis"
-          $exe = (Get-ChildItem $dir -Filter "*.exe")[0].FullName
-          $zip = $exe -replace '\.exe$', '.nsis.zip'
-          Compress-Archive -Path $exe -DestinationPath $zip -Force
-          npx tauri signer sign --private-key "$env:TAURI_SIGNING_PRIVATE_KEY" --password "$env:TAURI_SIGNING_PRIVATE_KEY_PASSWORD" $zip
-          gh release upload "app-v$env:VERSION" $zip "$zip.sig" --clobber
-
-      - name: sign and upload macOS bundle signature
-        if: matrix.settings.platform == 'macos-latest'
-        shell: bash
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          VERSION: ${{ needs.create-release.outputs.package_version }}
-        run: |
-          if [[ "${{ matrix.settings.args }}" == *"aarch64"* ]]; then
-            BUNDLE="src-tauri/target/aarch64-apple-darwin/release/bundle/macos/Psysonic.app.tar.gz"
-            SIG_NAME="Psysonic_aarch64.app.tar.gz.sig"
-          else
-            BUNDLE="src-tauri/target/x86_64-apple-darwin/release/bundle/macos/Psysonic.app.tar.gz"
-            SIG_NAME="Psysonic_x64.app.tar.gz.sig"
-          fi
-          npx tauri signer sign --private-key "$TAURI_SIGNING_PRIVATE_KEY" --password "$TAURI_SIGNING_PRIVATE_KEY_PASSWORD" "$BUNDLE"
-          cp "${BUNDLE}.sig" "$SIG_NAME"
-          gh release upload "app-v${VERSION}" "$SIG_NAME" --clobber
 
   build-linux:
     needs: create-release
@@ -213,32 +174,3 @@ jobs:
           find src-tauri/target/release/bundle \
             \( -name "*.deb" -o -name "*.rpm" \) \
             | xargs gh release upload "app-v${VERSION}" --clobber
-
-  generate-manifest:
-    needs: [create-release, build-macos-windows]
-    permissions:
-      contents: write
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v5
-      - name: setup node
-        uses: actions/setup-node@v5
-        with:
-          node-version: lts/*
-      - name: cache npm
-        uses: actions/cache@v4
-        with:
-          path: ~/.npm
-          key: ${{ runner.os }}-npm-${{ hashFiles('package-lock.json') }}
-          restore-keys: ${{ runner.os }}-npm-
-      - name: generate latest.json
-        env:
-          VERSION: ${{ needs.create-release.outputs.package_version }}
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: node scripts/generate-update-manifest.js
-      - name: upload latest.json
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: |
-          VERSION=${{ needs.create-release.outputs.package_version }}
-          gh release upload "app-v${VERSION}" latest.json --clobber