fix: handle forward-slash drive roots and UNC paths in validation

Broaden the trailing-slash exemption to recognize both C:\ and C:/ as
drive roots. Tighten the client-side absolute path check to require a
separator after the drive letter and accept UNC paths (\\server\share).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/api/browse-directory/__tests__/route.test.ts

@@ -32,11 +32,16 @@ describe("normalizeSelectedPath", () => {
       .toBe("C:\\Users\\guy");
   });
 
-  it("should preserve Windows drive root", () => {
+  it("should preserve Windows drive root with backslash", () => {
     expect(normalizeSelectedPath("C:\\", "win32"))
       .toBe("C:\\");
   });
 
+  it("should preserve Windows drive root with forward slash", () => {
+    expect(normalizeSelectedPath("C:/", "win32"))
+      .toBe("C:/");
+  });
+
   it("should preserve Unix root /", () => {
     expect(normalizeSelectedPath("/", "darwin"))
       .toBe("/");

src/app/api/browse-directory/route.ts

@@ -26,7 +26,7 @@ export function normalizeSelectedPath(selectedPath: string, platform: string): s
 
   // Remove trailing slash/backslash (except root paths like "/" or "C:\")
   if (selectedPath.length > 1 && (selectedPath.endsWith("/") || selectedPath.endsWith("\\"))) {
-    if (!(platform === "win32" && /^[A-Za-z]:\\$/.test(selectedPath))) {
+    if (!(platform === "win32" && /^[A-Za-z]:[\\\/]$/.test(selectedPath))) {
       selectedPath = selectedPath.slice(0, -1);
     }
   }

src/components/ProjectSetupModal.tsx

@@ -200,8 +200,8 @@ export function ProjectSetupModal({
     }
 
     const trimmedPath = directoryPath.trim();
-    if (!(trimmedPath.startsWith("/") || /^[A-Za-z]:/.test(trimmedPath))) {
-      setError("Project directory must be an absolute path (starting with / or a drive letter)");
+    if (!(trimmedPath.startsWith("/") || /^[A-Za-z]:[\\\/]/.test(trimmedPath) || trimmedPath.startsWith("\\\\"))) {
+      setError("Project directory must be an absolute path (starting with /, a drive letter, or a UNC path)");
       return;
     }
 

src/components/__tests__/ProjectSetupModal.test.tsx

@@ -407,7 +407,7 @@ describe("ProjectSetupModal", () => {
 
       await waitFor(() => {
         expect(
-          screen.getByText("Project directory must be an absolute path (starting with / or a drive letter)")
+          screen.getByText("Project directory must be an absolute path (starting with /, a drive letter, or a UNC path)")
         ).toBeInTheDocument();
       });
       expect(onSave).not.toHaveBeenCalled();