feat(completion): optimize ID prefix filtering and add completions to more commands

Improvements to shell completions from PR #935:

1. Add IDPrefix field to IssueFilter for efficient database-level filtering
   - Queries are now filtered at SQL level instead of fetching all issues
   - Updated sqlite, transaction, and memory stores to support IDPrefix

2. Add ValidArgsFunction to additional commands:
   - dep (add, remove, list, tree)
   - comments, comment (add)
   - delete
   - graph
   - label (add, remove, list)
   - duplicate, supersede
   - audit
   - move
   - relate, unrelate
   - refile
   - gate (show, resolve, add-waiter)

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

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

internal/storage/memory/memory.go

@@ -620,6 +620,11 @@ func (m *MemoryStorage) SearchIssues(ctx context.Context, query string, filter t
 			}
 		}
 
+		// ID prefix filtering (for shell completion)
+		if filter.IDPrefix != "" && !strings.HasPrefix(issue.ID, filter.IDPrefix) {
+			continue
+		}
+
 		// Parent filtering (bd-yqhh): filter children by parent issue
 		if filter.ParentID != nil {
 			isChild := false

internal/storage/sqlite/queries.go

@@ -1836,6 +1836,12 @@ func (s *SQLiteStorage) SearchIssues(ctx context.Context, query string, filter t
 		whereClauses = append(whereClauses, fmt.Sprintf("id IN (%s)", strings.Join(placeholders, ", ")))
 	}
 
+	// ID prefix filtering (for shell completion)
+	if filter.IDPrefix != "" {
+		whereClauses = append(whereClauses, "id LIKE ?")
+		args = append(args, filter.IDPrefix+"%")
+	}
+
 	// Wisp filtering
 	if filter.Ephemeral != nil {
 		if *filter.Ephemeral {

internal/storage/sqlite/transaction.go

@@ -1181,6 +1181,12 @@ func (t *sqliteTxStorage) SearchIssues(ctx context.Context, query string, filter
 		whereClauses = append(whereClauses, fmt.Sprintf("id IN (%s)", strings.Join(placeholders, ", ")))
 	}
 
+	// ID prefix filtering (for shell completion)
+	if filter.IDPrefix != "" {
+		whereClauses = append(whereClauses, "id LIKE ?")
+		args = append(args, filter.IDPrefix+"%")
+	}
+
 	// Wisp filtering
 	if filter.Ephemeral != nil {
 		if *filter.Ephemeral {