fix(#411): remediate frontend review findings — wire fetchWithRetry, fix error handling

- Wire fetchWithRetry into login page config fetch (was dead code)
- Remove duplicate ERROR_CODE_MESSAGES, use parseAuthError from auth-errors.ts
- Fix OAuth sign-in fire-and-forget: add .catch() with PDA error + loading reset
- Fix credential login catch: use parseAuthError for better error messages
- Add user feedback when auth config fetch fails (was silent degradation)
- Fix sign-out failure: use logAuthError and set authError state
- Enable fetchWithRetry production logging for retry visibility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/lib/auth/fetch-with-retry.test.ts

@@ -40,7 +40,6 @@ function mockResponse(status: number, ok?: boolean): Response {
 
 describe("fetchWithRetry", (): void => {
   const originalFetch = global.fetch;
-  const originalEnv = process.env.NODE_ENV;
   const sleepMock = vi.mocked(sleep);
 
   beforeEach((): void => {
@@ -52,7 +51,6 @@ describe("fetchWithRetry", (): void => {
   afterEach((): void => {
     vi.restoreAllMocks();
     global.fetch = originalFetch;
-    process.env.NODE_ENV = originalEnv;
   });
 
   it("should succeed on first attempt without retrying", async (): Promise<void> => {
@@ -203,8 +201,7 @@ describe("fetchWithRetry", (): void => {
     expect(recordedDelays).toEqual([1000, 2000, 4000]);
   });
 
-  it("should log retry attempts in development mode", async (): Promise<void> => {
-    process.env.NODE_ENV = "development";
+  it("should log retry attempts in all environments", async (): Promise<void> => {
     const warnSpy = vi.spyOn(console, "warn").mockImplementation((): void => {});
 
     const okResponse = mockResponse(200);
@@ -222,18 +219,22 @@ describe("fetchWithRetry", (): void => {
     warnSpy.mockRestore();
   });
 
-  it("should NOT log retry attempts in production mode", async (): Promise<void> => {
-    process.env.NODE_ENV = "production";
+  it("should log retry attempts for HTTP errors", async (): Promise<void> => {
     const warnSpy = vi.spyOn(console, "warn").mockImplementation((): void => {});
 
+    const serverError = mockResponse(500);
     const okResponse = mockResponse(200);
+
     vi.mocked(global.fetch)
-      .mockRejectedValueOnce(new TypeError("Failed to fetch"))
+      .mockResolvedValueOnce(serverError)
       .mockResolvedValueOnce(okResponse);
 
     await fetchWithRetry("https://api.example.com/auth/config");
 
-    expect(warnSpy).not.toHaveBeenCalled();
+    expect(warnSpy).toHaveBeenCalledTimes(1);
+    expect(warnSpy).toHaveBeenCalledWith(
+      expect.stringContaining("[Auth] Retry 1/3 after HTTP 500"),
+    );
 
     warnSpy.mockRestore();
   });