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/comments.go

@@ -218,11 +218,16 @@ func init() {
 	commentsCmd.AddCommand(commentsAddCmd)
 	commentsAddCmd.Flags().StringP("file", "f", "", "Read comment text from file")
 	commentsAddCmd.Flags().StringP("author", "a", "", "Add author to comment")
-	
+
 	// Add the same flags to the alias
 	commentCmd.Flags().StringP("file", "f", "", "Read comment text from file")
 	commentCmd.Flags().StringP("author", "a", "", "Add author to comment")
-	
+
+	// Issue ID completions
+	commentsCmd.ValidArgsFunction = issueIDCompletion
+	commentsAddCmd.ValidArgsFunction = issueIDCompletion
+	commentCmd.ValidArgsFunction = issueIDCompletion
+
 	rootCmd.AddCommand(commentsCmd)
 	rootCmd.AddCommand(commentCmd)
 }