Standardize warning output to use style.PrintWarning (gt-g6kor)

- Add PrintWarning helper in internal/style/style.go
- Update 35 warning message outputs across 16 files to use consistent format
- All warnings now display as "⚠ Warning: <message>" in yellow/bold

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/mq_submit.go

@@ -167,7 +167,7 @@ func runMqSubmit(cmd *cobra.Command, args []string) error {
 		fmt.Printf("%s Auto-cleanup: polecat work submitted\n", style.Bold.Render("✓"))
 		if err := polecatCleanup(rigName, worker, townRoot); err != nil {
 			// Non-fatal: warn but return success (MR was created)
-			fmt.Printf("%s Could not auto-cleanup: %v\n", style.Warning.Render("Warning:"), err)
+			style.PrintWarning("Could not auto-cleanup: %v", err)
 			fmt.Println(style.Dim.Render("  You may need to run 'gt handoff --shutdown' manually"))
 			return nil
 		}