Fix Windows build: remove lockfile before npm install

The lockfile was generated on Linux and doesn't include Windows
platform-specific optional deps (rollup, esbuild, etc). Delete
package-lock.json and node_modules so npm resolves fresh.

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

.gitea/workflows/build-app.yml

@@ -119,6 +119,8 @@ jobs:
         working-directory: ./app
         run: |
           set "PATH=%USERPROFILE%\.cargo\bin;C:\Program Files\nodejs;%PATH%"
+          if exist node_modules rmdir /s /q node_modules
+          if exist package-lock.json del package-lock.json
           npm install
 
       - name: Build Tauri app