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

cmd/bd/audit.go

@@ -160,6 +160,9 @@ func init() {
 	auditLabelCmd.Flags().StringVar(&auditLabelValue, "label", "", `Label value (e.g. "good" or "bad")`)
 	auditLabelCmd.Flags().StringVar(&auditLabelReason, "reason", "", "Reason for label")
 
+	// Issue ID completions
+	auditCmd.ValidArgsFunction = issueIDCompletion
+
 	auditCmd.AddCommand(auditRecordCmd)
 	auditCmd.AddCommand(auditLabelCmd)
 	rootCmd.AddCommand(auditCmd)