command-id-convention: trailing colon in multi-colon command IDs bypasses empty name check #159

Description

In the command-id-convention rule (src/rules/command-id-convention.ts), checking for an empty name segment uses separator === commandId.length - 1, where separator = commandId.indexOf(':').

Because indexOf(':') matches the first colon, this check only detects an empty name if the command ID contains exactly one colon (e.g. 'my-extension:'). Multi-colon command IDs with sub-namespaces (such as 'my-extension:sub:' or 'notebook:run-cell:') bypass the emptySegment check completely and silently pass without reporting an error.

Reproduce

1. Enable the jupyter/command-id-convention rule.
2. Lint code containing a command ID with multiple colons ending in a trailing colon:

   app.commands.addCommand('my-extension:sub:', {
     execute: () => {}
   });