fix(install): kill running muyue before extracting (v0.7.7)

User reported v0.7.6 install silently no-op'd when v0.7.5 was still
running:

  $dest = "$env:LOCALAPPDATA\Muyue"
  Expand-Archive -Path "$env:TEMP\muyue.zip" -DestinationPath $dest -Force
  # No error, but the running v0.7.5 .exe stays in place because
  # Windows refuses to overwrite a locked file. After 'install', the
  # 'muyue' command still launches v0.7.5.

Add a Stop-Process step at the top of the install snippet:

  Get-Process muyue, muyue-windows-amd64 -ErrorAction SilentlyContinue |
    Stop-Process -Force
  Start-Sleep -Milliseconds 500

-ErrorAction SilentlyContinue makes it idempotent (no error on a
clean first install). The 500ms sleep gives Windows time to release
the file handle before Expand-Archive opens the destination paths.

Snippet bumps to 6 lines; explanatory note added so users updating
from a previous version know why this step matters.

- internal/version/version.go: 0.7.6 → 0.7.7
- CHANGELOG.md: v0.7.7 entry

.gitea/workflows/ci-main.yml

@@ -152,12 +152,15 @@ jobs:
             echo ""
             echo "**Windows (x86_64)** — sans privilèges admin, crée les raccourcis Bureau + Menu Démarrer + commande \`muyue\` dans la session courante :"
             echo "\`\`\`powershell"
+            echo "Get-Process muyue, muyue-windows-amd64 -ErrorAction SilentlyContinue | Stop-Process -Force; Start-Sleep -Milliseconds 500"
             echo "\$dest = \"\$env:LOCALAPPDATA\\Muyue\"; New-Item -ItemType Directory -Force -Path \$dest | Out-Null"
             echo "Invoke-WebRequest -Uri \"${DL_URL}/muyue-windows-amd64.zip\" -OutFile \"\$env:TEMP\\muyue.zip\""
             echo "Expand-Archive -Path \"\$env:TEMP\\muyue.zip\" -DestinationPath \$dest -Force"
             echo "& \"\$dest\\muyue-windows-amd64.exe\" install-shortcuts"
             echo "\$env:Path += \";\$dest\""
             echo "\`\`\`"
+            echo ""
+            echo "Le 1ʳᵉ ligne tue toute instance Muyue déjà lancée (sinon Windows refuse d'écraser le \`.exe\` verrouillé et l'install échoue silencieusement). Si vous mettez à jour depuis une version précédente, c'est obligatoire."
           } > /tmp/stable_changelog.md
           echo "path=/tmp/stable_changelog.md" >> $GITHUB_OUTPUT