fix(ci): exclude xtask from cross-platform validation

xtask is a development-only tool that doesn't need to be cross-platform
compatible. Only validate crates in the crates/ directory.

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

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

Author: cloudbridgeuy

.github/workflows/ci.yml

@@ -82,7 +82,7 @@ jobs:
             ${{ runner.os }}-cargo-
 
       - name: Check compilation for ${{ matrix.target }}
-        run: cargo check --target ${{ matrix.target }} --verbose
+        run: cargo check --target ${{ matrix.target }} --workspace --exclude xtask --verbose
 
   unused-deps:
     name: Check Unused Dependencies