Add a branded header to CLI help

[HarshPopat23]

Summary

Replaces the minimal single-line CLI help header with a high-impact, branded ASCII-art header featuring both the official JSON Schema geometric octagonal logo and the Sourcemeta interwoven chevron emblem, styled with ANSI colors.

---

Commands Displaying the Logo Header

The branded logo header is rendered whenever help documentation is requested or displayed by default. Specifically, it appears on the following command invocations:

1. Zero-Argument Invocation (Default behavior):

   jsonschema

1. **Explicit Help Command:**:
   ```bash
  jsonschema help

1. Long Help Option :

   jsonschema --help

1. **Short Help Option** :
   ```bash
   jsonschema -h

[augmentcode]

🤖 Augment PR Summary

Summary: This PR replaces the compact CLI help title with a branded five-line ASCII banner.

Changes:

• Adds `print_help_header()` to render the JSON Schema and Sourcemeta marks, title, version, and tagline.
• Invokes the shared header from the global help command, including zero-argument invocation.
• Applies the existing bold-cyan terminal styling policy to banner marks and title.
• Updates help CLI fixtures for normal, short, long, forced-color, and no-argument help output.

_{🤖 Was this summary useful? React with 👍 or 👎}

[augmentcode]

Review completed. No suggestions at this time.

Comment augment review to trigger a new review at any time.

[jviotti]

@HarshPopat23 For these PRs do you mind showing a screenshot of how it looks like on your terminal? Just to make it a bit easier to review without having to clone, compile, and run myself :)

[cubic-dev-ai]

No issues found across 4 files

_{Re-trigger cubic}

[cubic-dev-ai]

All reported issues were addressed across 4 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[HarshPopat23]

@jviotti PTAL:

[jviotti]

The CLI does more than this though, and will do even more in the future. Can we keep this more generic and open-ended? Maybe take inspiration from how we describe it in the README and repo description?

[jviotti]

This ASCII art is huge. If we do some ASCII art it has to be relatively small. Also keep in mind that nowadays, people run this CLI a lot through LLMs, and you will probably consume a good amount of tokens parsing this massive ASCII art.

Maybe something simpler? It doesn't need to be the JSON Schema logo. Can be something else that looks cool

[HarshPopat23]

Hi @jviotti,

Thanks for the feedback.
I've updated the PR:

1. Compact & Token-Friendly: Simplified the ASCII art to a minimal, lightweight 3-row Sourcemeta chevron mark matching our official repo banner. It takes up minimal vertical space and consumes under 10 tokens for LLM parsing.
2. Generic & Open-Ended Tagline: Replaced the specific command list with the official description from the README/banner: "The CLI for working with JSON Schema, the world's most popular schema language."

Here is how it looks on the terminal:

[jviotti]

Nice! Looks super cool! Thanks for this!