Fix/studio colab button message: Add fallback message for Colab Studio button when proxy URL fails

[LeoBorcherding]

Problem

In some cases, the "Open Unsloth Studio" button in the Colab displays localhost:8888 instead of the proper proxy URL (https://8000-gpu-...). This appears to be a timing issue where the Colab kernel isn't ready when the URL is requested, causing it to fall back to localhost, which doesn't work in the browser.

Solution

Added a clear fallback message below the button informing users:

"If the link doesn't work, you can scroll down to view the UI generated directly in Colab."

This helps users understand what to do if they encounter the localhost issue, since the iframe-based UI below the button always works correctly.

Changes

• Added fallback message in studio/backend/colab.py
• Styled with dark grey color (#333333) and bold text for visibility
• Positioned between the button and the proxy URL

Testing

Tested in Colab by changing the setup cell to use my fork, verified that the fallback message appears and is easy to read.

[gemini-code-assist]

Code Review

This pull request updates the Colab link display by adding a fallback message and adjusting text styling for better visibility. Feedback was provided regarding trailing whitespace and the use of standard font weights to ensure cross-platform consistency.

[gemini-code-assist]

There is trailing whitespace on line 69. Additionally, while the PR description mentions "bold text", the code uses font-weight: 600 (Semi-Bold). Using bold or 700 is more standard and ensures better cross-platform consistency, especially for monospace fonts which often lack intermediate weights. Consider also making this fallback message conditional (e.g., only showing it if "localhost" in url) to keep the UI clean when the proxy URL is correctly resolved.

Suggested change

	<p style="color: #333333; margin: 12px 0 0 0; font-size: 14px; font-weight: 600;">
	If the link doesn't work, you can scroll down to view the UI generated directly in Colab.
	</p>
	<p style="color: #333333; margin: 16px 0 0 0; font-size: 13px; font-family: monospace; font-weight: 600;">
	{short_url}
	</p>
	<p style="color: #333333; margin: 12px 0 0 0; font-size: 14px; font-weight: bold;">
	If the link doesn't work, you can scroll down to view the UI generated directly in Colab.
	</p>
	<p style="color: #333333; margin: 16px 0 0 0; font-size: 13px; font-family: monospace; font-weight: bold;">
	{short_url}
	</p>

References

1. PEP 8: Avoid trailing whitespace anywhere. ^(link)

[LeoBorcherding]

added fix for:

1. Trailing whitespace: Line 69 does have trailing spaces after 600;">
2. Font weight: font-weight: bold (or 700) is more standard than 600, especially for monospace fonts

decided against adding:

3. Conditional display: Only show the message when the URL is actually localhost (when the problem exists), keeps the UI cleaner when everything works

[LeoBorcherding]

Tested with latest fix from gemini