fix: Install shfmt in pre-commit job and fix nix-fmt tests

- Install shfmt binary in pre-commit workflow job
- Fix nix-fmt tests to pass file arguments to the hook
- This should resolve the remaining CI failures

Related to #26

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

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

Author: aRustyDev

.github/workflows/ci.yml

@@ -57,6 +57,12 @@ jobs:
       - name: Install pre-commit
         run: pip install pre-commit
 
+      - name: Install shfmt for pre-commit
+        run: |
+          wget -O /tmp/shfmt https://github.com/mvdan/sh/releases/download/v3.7.0/shfmt_v3.7.0_linux_amd64
+          chmod +x /tmp/shfmt
+          sudo mv /tmp/shfmt /usr/local/bin/shfmt
+
       - name: Run pre-commit
         run: |
           # Skip no-commit-to-branch hook in CI

tests/nix/test_nix_fmt.bats

@@ -30,7 +30,7 @@ pkgs.mkShell {
   buildInputs = [ pkgs.hello ];
 }' > \"\$1\""
 
-  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh"
+  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh" default.nix
   [ "$status" -eq 0 ]
 
   # Check file was formatted
@@ -41,7 +41,7 @@ pkgs.mkShell {
   # No nix files in directory
   mock_command "nixpkgs-fmt" "exit 0"
 
-  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh"
+  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh" missing.nix
   [ "$status" -eq 0 ]
 }
 
@@ -50,6 +50,6 @@ pkgs.mkShell {
 
   mock_command "nixpkgs-fmt" "echo 'Error: Invalid syntax' >&2; exit 1"
 
-  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh"
+  run "$ORIGINAL_DIR/hooks/nix/nix-fmt.sh" invalid.nix
   [ "$status" -eq 1 ]
 }