fix: improve index command help menu formatting

- Move examples from description to addHelpText() so they only appear
  in Usage: ctxc index [options] [command]

Index a data source

Options:
  -h, --help           display help for command

Commands:
  github [options]     Index a GitHub repository
  gitlab [options]     Index a GitLab project
  bitbucket [options]  Index a Bitbucket repository
  website [options]    Crawl and index a website
  help [command]       display help for command, not in the main menu
- Simplify usage line to  instead of
  showing two separate usage patterns

Agent-Id: agent-8cab8bce-f29f-48f1-8fc1-86167ff2398b

Author: richhankins

src/bin/cmd-index.ts

@@ -273,7 +273,7 @@ urlCommand.action(async (url: string, options) => {
 
 // Main index command
 export const indexCommand = new Command("index")
-  .usage("<url> [options]\n       ctxc index <source> [options]")
+  .usage("<url | source> [options]")
   .description("Index a data source")
   .addHelpText('after', `
 Examples: