fix(ci): fix Windows build path and add Taskfile to CI

- Use npm --prefix for beforeBuildCommand/beforeDevCommand since Tauri
  runs these from projectPath (crates/mt-tauri/), not repo root
- Add go-task/setup-task@v1 to setup-tauri-build action

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

Author: pythoninthegrass

.github/actions/setup-tauri-build/action.yml

@@ -37,6 +37,9 @@ runs:
         choco install cmake --installargs 'ADD_CMAKE_TO_PATH=System' -y
         choco install rustup.install -y
 
+    - name: Install Task
+      uses: go-task/setup-task@v1
+
     - name: Setup Node.js
       uses: actions/setup-node@v6
       with:

crates/mt-tauri/tauri.conf.json

@@ -4,8 +4,8 @@
   "version": "0.1.0",
   "identifier": "com.mt.desktop",
   "build": {
-    "beforeDevCommand": "npm run dev",
-    "beforeBuildCommand": "npm run build",
+    "beforeDevCommand": "npm --prefix ../../app/frontend run dev",
+    "beforeBuildCommand": "npm --prefix ../../app/frontend run build",
     "devUrl": "http://localhost:5173",
     "frontendDist": "../../app/frontend/dist"
   },