feat: add gate issue type and CLI commands for async coordination (bd-udsi)

Add async gates - coordination primitives for agents to wait on external events
like CI completion, PR merges, timers, or human approval.

Changes:
- Add 'gate' issue type to types.go with gate-specific fields:
  - AwaitType: condition type (gh:run, gh:pr, timer, human, mail)
  - AwaitID: condition identifier
  - Timeout: max wait duration
  - Waiters: mail addresses to notify when gate clears
- Add SQLite migration 027_gate_columns for new fields
- Update all SQLite storage queries to handle gate fields
- Add bd gate commands: create, show, list, close, wait
- All commands support --json output and --no-daemon mode

Closes: bd-2v0f, bd-lz49, bd-u66e

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

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

cmd/bd/show.go

@@ -527,7 +527,7 @@ var updateCmd = &cobra.Command{
 			issueType, _ := cmd.Flags().GetString("type")
 			// Validate issue type
 			if !types.IssueType(issueType).IsValid() {
-				fmt.Fprintf(os.Stderr, "Error: invalid issue type %q. Valid types: bug, feature, task, epic, chore\n", issueType)
+				fmt.Fprintf(os.Stderr, "Error: invalid issue type %q. Valid types: bug, feature, task, epic, chore, merge-request, molecule, gate\n", issueType)
 				os.Exit(1)
 			}
 			updates["issue_type"] = issueType
@@ -1390,7 +1390,7 @@ func init() {
 	updateCmd.Flags().StringP("status", "s", "", "New status")
 	registerPriorityFlag(updateCmd, "")
 	updateCmd.Flags().String("title", "", "New title")
-	updateCmd.Flags().StringP("type", "t", "", "New type (bug|feature|task|epic|chore|merge-request|molecule)")
+	updateCmd.Flags().StringP("type", "t", "", "New type (bug|feature|task|epic|chore|merge-request|molecule|gate)")
 	registerCommonIssueFlags(updateCmd)
 	updateCmd.Flags().String("notes", "", "Additional notes")
 	updateCmd.Flags().String("acceptance-criteria", "", "DEPRECATED: use --acceptance")