fix: remove todo placeholders from CLI help text

[Copilot]

CLI help displayed TODO placeholders instead of proper descriptions for the root and check commands.

Changes

Root command (cmd/root.go)

• Short: "A fast, concurrent broken link checker for websites and sitemaps"
• Long: Description aligned with README explaining validation of links during development with concurrent checking and color-coded output

Check command (cmd/check.go)

• Short: "Check links on a URL or sitemap"
• Long: Description of link validation with status code checks and colored results

All descriptions sourced from existing README to maintain consistency across documentation.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• invalid-domain-that-does-not-exist-12345.com
  • Triggering command: /tmp/go-build1037829153/b204/checker.test -test.testlogfile=/tmp/go-build1037829153/b204/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Remove and fix TODO items in --help</issue_title>
<issue_description>TODO items remain in the cli help.

TODO: Add a longer description here

Usage:
  brokli [flags]
  brokli [command]

Available Commands:
  check       TODO: Add a short description here
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  version     Print the version number of Brokli

Flags:
  -h, --help      help for brokli
  -v, --version   version for brokli

Use "brokli [command] --help" for more information about a command.
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Remove and fix TODO items in --help #15

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