fix(claude): add interleaved-thinking beta header, AMP gzip error decoding, normalizeClaudeBudget max_tokens

1. Always include interleaved-thinking-2025-05-14 beta header so that
   thinking blocks are returned correctly for all Claude models.

2. Remove status-code guard in AMP reverse proxy ModifyResponse so that
   error responses (4xx/5xx) with hidden gzip encoding are decoded
   properly — prevents garbled error messages reaching the client.

3. In normalizeClaudeBudget, when the adjusted budget falls below the
   model minimum, set max_tokens = budgetTokens+1 instead of leaving
   the request unchanged (which causes a 400 from the API).

internal/runtime/executor/claude_executor.go

@@ -832,6 +832,9 @@ func applyClaudeHeaders(r *http.Request, auth *cliproxyauth.Auth, apiKey string,
 			baseBetas += ",oauth-2025-04-20"
 		}
 	}
+	if !strings.Contains(baseBetas, "interleaved-thinking") {
+		baseBetas += ",interleaved-thinking-2025-05-14"
+	}
 
 	hasClaude1MHeader := false
 	if ginHeaders != nil {