ci: move Linux build workflow to repo root .github/workflows/

Previous location (posimai-guard-app/.github/workflows/) was wrong —
GitHub Actions only reads .github/workflows/ at repository root.
Renamed to build-guard-linux.yml, added working-directory default.

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

.github/workflows/build-guard-linux.yml

@@ -1,15 +1,19 @@
-name: Build Linux
+name: Build Guard Linux
 
 on:
-  workflow_dispatch:   # 手動実行
+  workflow_dispatch:    # 手動実行
   push:
     tags:
-      - 'v*'           # v1.0.0 など tag push で自動実行
+      - 'guard-v*'      # guard-v0.1.0 など tag push で自動実行
 
 jobs:
   build-linux:
     runs-on: ubuntu-22.04
 
+    defaults:
+      run:
+        working-directory: posimai-guard-app
+
     steps:
       - uses: actions/checkout@v4
 
@@ -31,7 +35,7 @@ jobs:
       - name: Cache Rust
         uses: Swatinem/rust-cache@v2
         with:
-          workspaces: src-tauri
+          workspaces: posimai-guard-app/src-tauri
 
       - name: Install Node.js
         uses: actions/setup-node@v4
@@ -43,22 +47,19 @@ jobs:
 
       - name: Build Tauri (Linux)
         run: npm run build
-        env:
-          TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
-          TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
 
       - name: Upload .deb
         uses: actions/upload-artifact@v4
         with:
           name: posimai-guard-linux-deb
-          path: src-tauri/target/release/bundle/deb/*.deb
+          path: posimai-guard-app/src-tauri/target/release/bundle/deb/*.deb
           if-no-files-found: warn
 
       - name: Upload .AppImage
         uses: actions/upload-artifact@v4
         with:
           name: posimai-guard-linux-appimage
-          path: src-tauri/target/release/bundle/appimage/*.AppImage
+          path: posimai-guard-app/src-tauri/target/release/bundle/appimage/*.AppImage
           if-no-files-found: warn
 
       - name: Create GitHub Release (on tag)
@@ -66,7 +67,7 @@ jobs:
         uses: softprops/action-gh-release@v2
         with:
           files: |
-            src-tauri/target/release/bundle/deb/*.deb
-            src-tauri/target/release/bundle/appimage/*.AppImage
+            posimai-guard-app/src-tauri/target/release/bundle/deb/*.deb
+            posimai-guard-app/src-tauri/target/release/bundle/appimage/*.AppImage
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}