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/gate.go

@@ -871,6 +871,11 @@ func init() {
 	gateCheckCmd.Flags().BoolP("escalate", "e", false, "Escalate failed/expired gates")
 	gateCheckCmd.Flags().IntP("limit", "l", 100, "Limit results (default 100)")
 
+	// Issue ID completions
+	gateShowCmd.ValidArgsFunction = issueIDCompletion
+	gateResolveCmd.ValidArgsFunction = issueIDCompletion
+	gateAddWaiterCmd.ValidArgsFunction = issueIDCompletion
+
 	// Add subcommands
 	gateCmd.AddCommand(gateListCmd)
 	gateCmd.AddCommand(gateShowCmd)