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/browser/fetch.go

@@ -3,6 +3,7 @@ package browser
 import (
 	"context"
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"strings"
@@ -55,10 +56,12 @@ func FetchViaChrome(url string) ([]byte, error) {
 	defer timeoutCancel()
 
 	// Navigate and wait for Cloudflare challenge to resolve.
-	// Poll the page content until we get valid JSON (not the challenge page).
+	log.Printf("chrome-fetch: navigating to %s (profile: %s)", url, profileDir)
 	if err := chromedp.Run(ctx, chromedp.Navigate(url)); err != nil {
+		log.Printf("chrome-fetch: navigate failed: %v", err)
 		return nil, fmt.Errorf("chromedp navigate: %w", err)
 	}
+	log.Printf("chrome-fetch: navigation complete, polling for JSON...")
 
 	// Poll for JSON response — Cloudflare challenge takes a few seconds to clear
 	ticker := time.NewTicker(1 * time.Second)
@@ -82,15 +85,23 @@ func FetchViaChrome(url string) ([]byte, error) {
 			}
 			body = strings.TrimSpace(body)
 			if body == "" {
+				log.Printf("chrome-fetch: page body empty, waiting...")
 				continue
 			}
 			// Check if we got actual JSON (starts with [ or {), not a challenge page
 			if body[0] == '[' || body[0] == '{' {
+				log.Printf("chrome-fetch: got JSON response (%d bytes)", len(body))
 				// Also extract any fresh cookies for future plain HTTP attempts
 				_ = extractAndSaveCookies(ctx)
 				cancel() // graceful close, flushes cookies to profile
 				return []byte(body), nil
 			}
+			// Log a snippet of what we got (challenge page, login redirect, etc.)
+			snippet := body
+			if len(snippet) > 200 {
+				snippet = snippet[:200]
+			}
+			log.Printf("chrome-fetch: non-JSON body (%d bytes): %s", len(body), snippet)
 		}
 	}
 }