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>

internal/storage/sqlite/transaction.go

@@ -306,7 +306,8 @@ func (t *sqliteTxStorage) GetIssue(ctx context.Context, id string) (*types.Issue
 		       created_at, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
 		       deleted_at, deleted_by, delete_reason, original_type,
-		       sender, ephemeral, pinned, is_template
+		       sender, ephemeral, pinned, is_template,
+		       await_type, await_id, timeout_ns, waiters
 		FROM issues
 		WHERE id = ?
 	`, id)
@@ -1122,7 +1123,8 @@ func (t *sqliteTxStorage) SearchIssues(ctx context.Context, query string, filter
 		       created_at, updated_at, closed_at, external_ref,
 		       compaction_level, compacted_at, compacted_at_commit, original_size, source_repo, close_reason,
 		       deleted_at, deleted_by, delete_reason, original_type,
-		       sender, ephemeral, pinned, is_template
+		       sender, ephemeral, pinned, is_template,
+		       await_type, await_id, timeout_ns, waiters
 		FROM issues
 		%s
 		ORDER BY priority ASC, created_at DESC
@@ -1169,6 +1171,11 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 	var pinned sql.NullInt64
 	// Template field (beads-1ra)
 	var isTemplate sql.NullInt64
+	// Gate fields (bd-udsi)
+	var awaitType sql.NullString
+	var awaitID sql.NullString
+	var timeoutNs sql.NullInt64
+	var waiters sql.NullString
 
 	err := row.Scan(
 		&issue.ID, &contentHash, &issue.Title, &issue.Description, &issue.Design,
@@ -1178,6 +1185,7 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 		&issue.CompactionLevel, &compactedAt, &compactedAtCommit, &originalSize, &sourceRepo, &closeReason,
 		&deletedAt, &deletedBy, &deleteReason, &originalType,
 		&sender, &wisp, &pinned, &isTemplate,
+		&awaitType, &awaitID, &timeoutNs, &waiters,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to scan issue: %w", err)
@@ -1239,6 +1247,19 @@ func scanIssueRow(row scanner) (*types.Issue, error) {
 	if isTemplate.Valid && isTemplate.Int64 != 0 {
 		issue.IsTemplate = true
 	}
+	// Gate fields (bd-udsi)
+	if awaitType.Valid {
+		issue.AwaitType = awaitType.String
+	}
+	if awaitID.Valid {
+		issue.AwaitID = awaitID.String
+	}
+	if timeoutNs.Valid {
+		issue.Timeout = time.Duration(timeoutNs.Int64)
+	}
+	if waiters.Valid && waiters.String != "" {
+		issue.Waiters = parseJSONStringArray(waiters.String)
+	}
 
 	return &issue, nil
 }