fix Windows build: make cargo visible in msys2 shell

The Rust toolchain is installed in the Windows PATH but not visible
from the msys2 shell. Explicitly add cargo to PATH and use per-step
shell selection instead of a job-level default.

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

Author: joske

.github/workflows/publish.yml

@@ -129,9 +129,6 @@ jobs:
     runs-on: windows-latest
     permissions:
       contents: write
-    defaults:
-      run:
-        shell: msys2 {0}
     steps:
       - name: Setup MSYS2
         uses: msys2/setup-msys2@v2
@@ -147,14 +144,19 @@ jobs:
       - name: Install Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1
       - name: Build release binary
-        run: cargo build --release
+        shell: msys2 {0}
+        run: |
+          export PATH="/c/Users/runneradmin/.cargo/bin:$PATH"
+          cargo build --release
       - name: Bundle binary with DLLs
+        shell: msys2 {0}
         run: |
           mkdir -p dist
           cp target/release/mergers.exe dist/
           # Copy all required DLLs from MSYS2
           ldd target/release/mergers.exe | grep "ucrt64" | awk '{print $3}' | xargs -I{} cp {} dist/
           # Copy GtkSourceView language specs and styles
+          mkdir -p dist/share
           cp -r /$MSYSTEM/share/gtksourceview-5 dist/share/gtksourceview-5
           # Copy GTK schema files
           mkdir -p dist/share/glib-2.0/schemas
@@ -164,6 +166,7 @@ jobs:
           cp -r /$MSYSTEM/share/icons/hicolor dist/share/icons/
           cp -r /$MSYSTEM/share/icons/Adwaita dist/share/icons/ 2>/dev/null || true
       - name: Create zip
+        shell: msys2 {0}
         run: |
           cd dist
           7z a ../mergers-windows-x86_64.zip ./*