Fix #97: Add daemon mode check to rename-prefix command

- Prevents nil pointer dereference when daemon is active
- Ensures direct mode or fails gracefully
- Lower Python requirement to 3.10+ for beads-mcp (#99)

Amp-Thread-ID: https://ampcode.com/threads/T-740c6f9c-b8f0-4155-8bfa-7075eea2df22
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/rename_prefix.go

@@ -35,6 +35,19 @@ Example:
 
 		ctx := context.Background()
 
+		// rename-prefix requires direct mode (not supported by daemon)
+		if daemonClient != nil {
+			if err := ensureDirectMode("daemon does not support rename-prefix command"); err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				os.Exit(1)
+			}
+		} else if store == nil {
+			if err := ensureStoreActive(); err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				os.Exit(1)
+			}
+		}
+
 		if err := validatePrefix(newPrefix); err != nil {
 			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 			os.Exit(1)