Add diagnostic logging to Chrome fallback

Log navigation, polling state, and response snippets so we can
diagnose whether the fallback fails due to Cloudflare challenge,
login redirect, profile lock, or other issues.

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

internal/fetcher/fetcher.go

@@ -102,11 +102,13 @@ func fetchWithFallback(url, sessionKey string) ([]byte, error) {
 	}
 	if status == 403 {
 		// Likely a Cloudflare JS challenge — fall back to headless Chrome
-		log.Printf("HTTP 403 for %s, falling back to headless Chrome", url)
+		log.Printf("HTTP 403 for %s, falling back to Chrome", url)
 		chromeBody, chromeErr := browser.FetchViaChrome(url)
 		if chromeErr != nil {
-			return nil, fmt.Errorf("auth_expired") // treat as auth failure if Chrome also fails
+			log.Printf("Chrome fallback failed: %v", chromeErr)
+			return nil, fmt.Errorf("auth_expired")
 		}
+		log.Printf("Chrome fallback succeeded (%d bytes)", len(chromeBody))
 		return chromeBody, nil
 	}
 	return nil, fmt.Errorf("HTTP %d", status)