ci: Change Linux target from musl to gnu for GTK compatibility

Switch from x86_64-unknown-linux-musl to x86_64-unknown-linux-gnu target
for Linux builds. The musl target fails for Dioxus desktop apps because
GTK libraries require glibc and cross-compilation setup that's not available
in the GitHub Actions environment.

Also remove musl-tools dependency since we're now using the standard GNU libc target.

prompts:
- Run cargo build --release --target x86_64-unknown-linux-musl --package markdown-neuraxis-dioxus (followed by pkg-config cross-compilation error)
- use ci: prefix for all ci yml

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: timabell

.github/workflows/_ci.yml

@@ -79,7 +79,7 @@ jobs:
       matrix:
         include:
           - runner: ubuntu-latest
-            target: x86_64-unknown-linux-musl
+            target: x86_64-unknown-linux-gnu
             os: linux
           - runner: windows-latest
             target: x86_64-pc-windows-msvc
@@ -107,7 +107,7 @@ jobs:
         if: matrix.os == 'linux'
         run: |
           sudo apt-get update
-          sudo apt-get install -y pkg-config libssl-dev libgtk-3-dev libayatana-appindicator3-dev librsvg2-dev libwebkit2gtk-4.1-dev musl-tools
+          sudo apt-get install -y pkg-config libssl-dev libgtk-3-dev libayatana-appindicator3-dev librsvg2-dev libwebkit2gtk-4.1-dev
 
       - name: Install macOS dependencies
         if: startsWith(matrix.os, 'macos')