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/search.go

@@ -373,7 +373,7 @@ func init() {
 	searchCmd.Flags().String("query", "", "Search query (alternative to positional argument)")
 	searchCmd.Flags().StringP("status", "s", "", "Filter by status (open, in_progress, blocked, deferred, closed)")
 	searchCmd.Flags().StringP("assignee", "a", "", "Filter by assignee")
-	searchCmd.Flags().StringP("type", "t", "", "Filter by type (bug, feature, task, epic, chore)")
+	searchCmd.Flags().StringP("type", "t", "", "Filter by type (bug, feature, task, epic, chore, merge-request, molecule, gate)")
 	searchCmd.Flags().StringSliceP("label", "l", []string{}, "Filter by labels (AND: must have ALL)")
 	searchCmd.Flags().StringSlice("label-any", []string{}, "Filter by labels (OR: must have AT LEAST ONE)")
 	searchCmd.Flags().IntP("limit", "n", 50, "Limit results (default: 50)")