fix: Windows path compatibility in resolver tests (Fission-AI#524)

- Use path.join() in test expectations instead of hardcoded forward slashes
- Add openspec/config.yaml with cross-platform requirements to prevent
  similar issues in future proposals

The tests were failing on Windows because path.join() uses backslashes
on Windows, but the test expectations hardcoded forward slashes.

Author: TabishB

openspec/config.yaml

@@ -0,0 +1,24 @@
+schema: spec-driven
+
+context: |
+  Tech stack: TypeScript, Node.js (≥20.19.0), ESM modules
+  Package manager: pnpm
+  CLI framework: Commander.js
+
+  Cross-platform requirements:
+  - This tool runs on macOS, Linux, AND Windows
+  - Always use path.join() or path.resolve() for file paths - never hardcode slashes
+  - Never assume forward-slash path separators
+  - Tests must use path.join() for expected path values, not hardcoded strings
+  - Consider case sensitivity differences in file systems
+
+rules:
+  specs:
+    - Include scenarios for Windows path handling when dealing with file paths
+    - Requirements involving paths must specify cross-platform behavior
+  tasks:
+    - Add Windows CI verification as a task when changes involve file paths
+    - Include cross-platform testing considerations
+  design:
+    - Document any platform-specific behavior or limitations
+    - Prefer Node.js path module over string manipulation for paths

test/core/artifact-graph/resolver.test.ts

@@ -335,12 +335,12 @@ version: [[[invalid yaml
     it('should return correct path', () => {
       const projectRoot = '/path/to/project';
       const schemasDir = getProjectSchemasDir(projectRoot);
-      expect(schemasDir).toBe('/path/to/project/openspec/schemas');
+      expect(schemasDir).toBe(path.join('/path/to/project', 'openspec', 'schemas'));
     });
 
     it('should work with relative-looking paths', () => {
       const schemasDir = getProjectSchemasDir('./my-project');
-      expect(schemasDir).toBe('my-project/openspec/schemas');
+      expect(schemasDir).toBe(path.join('my-project', 'openspec', 'schemas'));
     });
   });