docs: add hero banner to README

[gdespirito]

Adds the hero banner to the README, replacing the <!-- banner --> placeholder left in #23.

The image is hosted as an attachment on issue #25, so no binaries are added to the git history.

Preview:

🤖 Generated with Claude Code

https://claude.ai/code/session_01WvDYWr2Tx3diCV3NXGrKRX

Summary by CodeRabbit

• Documentation
  • Added a centered banner image to the README.
  • Removed the previous placeholder banner comment.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3052d1f4-795b-4b36-8edd-67c6d5addc2f

📥 Commits

Reviewing files that changed from the base of the PR and between 46f8f7d and 7eca9ea.

📒 Files selected for processing (1)

• README.md

---

📝 Walkthrough

Walkthrough

The README now begins with a centered banner image, replacing the previous placeholder comment.

Changes

README Presentation

Layer / File(s)	Summary
Add centered README banner README.md	Replaces the top placeholder banner comment with a centered HTML image block.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding a hero banner to the README.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch readme-banner

---

_{Comment @coderabbitai help to get the list of available commands.}