docs: update README banner

[jannikmaierhoefer]

Replaced GitHub banner image with a new hero image.

Greptile Summary

This PR replaces the old GitHub banner markdown image with an HTML <img> tag pointing to a new hero image asset hosted on GitHub. This is a pure documentation change with no code impact.

• The new <img> tag explicitly sets width="2400" and height="600", which helps browsers reserve layout space before the image loads.
• The alt attribute is currently "hero-b" (an internal asset name) rather than a meaningful description — worth updating for accessibility.

Confidence Score: 5/5

Documentation-only change swapping a banner image — no code paths affected, safe to merge.

The change touches only the README banner image, switching from markdown syntax to an HTML img tag. The only minor observation is the non-descriptive alt text "hero-b".

No files require special attention.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[README.md] -->|Before| B["![GitHub Banner]\nMarkdown image syntax\nAsset: assets/2834609/d1613347"]
    A -->|After| C["<img> HTML tag\nwidth=2400 height=600\nAsset: user-attachments/d78fe000\nalt='hero-b'"]

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
README.md:1
The `alt` attribute is set to `"hero-b"`, which appears to be an internal asset name rather than a meaningful description. Screen readers and users with images disabled will read this value literally, providing no useful context about the image content.

```suggestion
<img width="2400" height="600" alt="Langfuse hero image" src="https://github.com/user-attachments/assets/d78fe000-209b-4e18-8c46-c73410559cec" />
```

_{Reviews (1): Last reviewed commit: "docs: update README banner" | Re-trigger Greptile}

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Project	Deployment	Actions	Updated (UTC)
langfuse-js	Ready	Preview	Jun 1, 2026 2:04pm

[github-actions]

@claude review

[claude]

LGTM, simple README banner image swap.

Extended reasoning...

Overview

This PR replaces a single image tag in README.md, swapping the old GitHub-hosted banner asset for a new hero image. No code, configuration, or build files are touched.

Security risks

None. This is a documentation-only change. The new image URL points to GitHub's user-attachments domain, which is the same trust boundary as the previous asset.

Level of scrutiny

Minimal scrutiny is appropriate. Docs/asset changes carry no runtime impact and cannot affect users of the published packages.

Other factors

The bug hunting system found nothing, and the change is a one-line, purely cosmetic README edit. Safe to shadow-approve.