Add argument support to /handoff command

Now supports: /handoff let's continue with feature X

Uses Claude Code's $ARGUMENTS placeholder to pass user's
message to gt handoff --cycle -m flag.

.claude/commands/handoff.md

@@ -1,12 +1,15 @@
 ---
 description: Hand off to fresh session, work continues from hook
-allowed-tools: Bash(gt handoff)
+allowed-tools: Bash(gt handoff:*)
+argument-hint: [message]
 ---
 
-Execute `gt handoff` to hand off to a fresh session:
+Hand off to a fresh session.
 
-```bash
-gt handoff
-```
+User's handoff message (if any): $ARGUMENTS
+
+Execute the appropriate command:
+- If user provided a message: `gt handoff --cycle -m "USER_MESSAGE_HERE"`
+- If no message provided: `gt handoff --cycle`
 
 End watch. A new session takes over, picking up any molecule on the hook.