fix(providers): replace HTTP-specific regex with standalone status code matcher

The precompiled HTTP regex used uppercase "HTTP" which never matched
because ClassifyError lowercases the input. Replace it with a
case-insensitive word-boundary pattern that matches any standalone
3-digit status code (300-599), which also subsumes the HTTP/x.x case.

Add test case for standalone status code extraction.

pkg/providers/error_classifier.go

@@ -9,7 +9,7 @@ import (
 // Common patterns in Go HTTP error messages
 var httpStatusPatterns = []*regexp.Regexp{
 	regexp.MustCompile(`status[:\s]+(\d{3})`),
-	regexp.MustCompile(`HTTP[/\s]+\d*\.?\d*\s+(\d{3})`),
+	regexp.MustCompile(`\b([3-5]\d{2})\b`),
 }
 
 // errorPattern defines a single pattern (string or regex) for error classification.
@@ -204,7 +204,7 @@ func classifyByMessage(msg string) FailoverReason {
 }
 
 // extractHTTPStatus extracts an HTTP status code from an error message.
-// Looks for patterns like "status: 429", "status 429", "HTTP 429", or standalone "429".
+// Looks for patterns like "status: 429", "status 429", "HTTP/1.1 429", "HTTP 429", or standalone "429".
 func extractHTTPStatus(msg string) int {
 	for _, p := range httpStatusPatterns {
 		if m := p.FindStringSubmatch(msg); len(m) > 1 {

pkg/providers/error_classifier_test.go

@@ -306,6 +306,7 @@ func TestExtractHTTPStatus(t *testing.T) {
 		{"status: 429 rate limited", 429},
 		{"status 401 unauthorized", 401},
 		{"HTTP/1.1 502 Bad Gateway", 502},
+		{"error 429", 429},
 		{"no status code here", 0},
 		{"random number 12345", 0},
 	}