fix: resolve relative paths against allowed directories instead of process.cwd()

Fixes issue where relative paths were incorrectly resolved against process.cwd(),
causing "Access denied - path outside allowed directories" errors when the MCP
server's working directory was outside the configured allowed directories.

The fix implements intelligent path resolution that:
1. First tries to resolve relative paths against each allowed directory
2. Validates the resulting path is within allowed directories
3. Falls back to the first allowed directory if no valid resolution is found
4. Maintains backward compatibility by falling back to process.cwd() when no allowed directories are configured

Resolves #2526

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

Co-authored-by: Ola Hungerford <olaservo@users.noreply.github.com>

src/filesystem/__tests__/lib.test.ts

@@ -204,6 +204,30 @@ describe('Lib Functions', () => {
         await expect(validatePath(newFilePath))
           .rejects.toThrow('Parent directory does not exist');
       });
+
+      it('resolves relative paths against allowed directories instead of process.cwd()', async () => {
+        const relativePath = 'test-file.txt';
+        const originalCwd = process.cwd;
+        
+        // Mock process.cwd to return a directory outside allowed directories
+        const disallowedCwd = process.platform === 'win32' ? 'C:\\Windows\\System32' : '/root';
+        (process as any).cwd = jest.fn(() => disallowedCwd);
+        
+        try {
+          const result = await validatePath(relativePath);
+          
+          // Result should be resolved against first allowed directory, not process.cwd()
+          const expectedPath = process.platform === 'win32' 
+            ? path.resolve('C:\\Users\\test', relativePath)
+            : path.resolve('/home/user', relativePath);
+          
+          expect(result).toBe(expectedPath);
+          expect(result).not.toContain(disallowedCwd);
+        } finally {
+          // Restore original process.cwd
+          process.cwd = originalCwd;
+        }
+      });
     });
   });