feat: add automatic streaming detection for piped input

- Automatically use streaming mode when stdin is piped
- No need to specify 'stream' command explicitly
- Simplifies usage: cat file.txt | tokenizer llama3
- Still supports explicit stream command for clarity
- Updates documentation to show both methods

The tokenizer now intelligently detects its context:
- With args: encode mode
- With piped input: stream mode
- Neither: show usage

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: jackspirou

llama3/cmd/llama3/command.go

@@ -2,6 +2,8 @@
 package llama3cmd
 
 import (
+	"os"
+
 	"github.com/spf13/cobra"
 )
 
@@ -31,9 +33,12 @@ Available commands:
   # Decode tokens
   tokenizer llama3 decode 128000 9906 11 1917 0 128001
   
-  # Stream from stdin
+  # Stream from stdin (explicit)
   cat large_file.txt | tokenizer llama3 stream
   
+  # Stream from stdin (implicit - automatic)
+  cat large_file.txt | tokenizer llama3
+  
   # Show tokenizer info
   tokenizer llama3 info`,
 		Args: cobra.ArbitraryArgs,
@@ -61,7 +66,15 @@ Available commands:
 				return encodeCmd.Execute()
 			}
 
-			// No args provided, show usage
+			// No args provided - check if stdin is piped
+			stat, _ := os.Stdin.Stat()
+			if (stat.Mode() & os.ModeCharDevice) == 0 {
+				// Data is being piped to stdin, use streaming mode
+				streamCmd := newStreamCmd()
+				return streamCmd.Execute()
+			}
+
+			// No args and no piped input, show usage
 			return cmd.Usage()
 		},
 	}