fix(httpclient): raise image-host upload deadline to 120s

The whole-request deadline for image hosting was 60s. A 2160p screenshot
failed against reelflix with:

  Post "https://img.reelflix.cc/api/1/upload": context deadline exceeded
  (Client.Timeout exceeded while awaiting headers)

"while awaiting headers" means the body was already sent and the deadline
expired waiting on the host to answer, so this is host processing time
rather than local transfer. The same batch reported
mean_attempt_duration=42.02s across 6 attempts, and since failed attempts
are timed too, the 5 successes averaged around 38s. That leaves barely
1.5x headroom against a 60s ceiling for an operation with a long tail.

120s restores roughly 3x headroom. UploadTimeout is consumed only by
internal/imagehosting; every tracker upload path uses DefaultTimeout, so
this does not widen any other deadline.

Author: nitrobass24

internal/httpclient/httpclient.go

@@ -11,7 +11,12 @@ import (
 const (
 	// DefaultTimeout and UploadTimeout are whole-request deadlines assigned to [http.Client.Timeout].
 	DefaultTimeout = 45 * time.Second
-	UploadTimeout  = 60 * time.Second
+	// UploadTimeout covers image-host uploads, where the deadline spans the host
+	// processing a multi-megabyte image and not just the transfer. 2160p
+	// screenshots run 5-8MB and hosts have been observed answering well past a
+	// minute under load, so this keeps roughly three times the headroom over
+	// their typical response time.
+	UploadTimeout = 120 * time.Second
 )
 
 // New returns a client whose timeout defaults to [DefaultTimeout] when timeout is non-positive.