Add validation to display name input

[AndyMcGN]

Describe briefly what this PR is doing and why.

Completes this issue about the lack of validation of the display name during sign up.

Testing

Explain how you tested this PR and give clear steps so the reviewer can replicate.

Backend checklist

• Added tests for any new code or added a regression test if fixing a bug
• Run the backend locally and it works
• Added migrations if there are any database changes, rebased onto develop if necessary for linear migration history

Web frontend checklist

• There are no console warnings when running the app
• Added tests where relevant
• Clicked around my changes running locally and it works
• Checked Desktop, Mobile and Tablet screen sizes

For maintainers

• Maintainers can push commits to my branch
• Maintainers can merge this PR for me

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Project	Deployment	Actions	Updated (UTC)
couchers	Ready	Preview	Mar 16, 2026 11:44am

[nabramow]

Ah sorry ignore what I wrote, I thought this was username at first as we have a ticket for that too.

[nabramow]

Okay this is almost there, thanks for picking this up @AndyMcGN!

I think we should also disallow numbers entirely for display name as well and only allow lowercase and capital letters and spaces. Right now I can start with a number and it's not giving me any error:

[nabramow]

Suggested change

	"invalid_characters_error": "Name can only contain letters, numbers, spaces, hyphens, and apostrophes",
	"invalid_characters_error": "Name can only contain letters, spaces, hyphens, and apostrophes",

Let's do this and remove the numbers!

[AndyMcGN]

@nabramow thanks for reviewing! Just to be clear, you're saying we should remove 'numbers, ' from the string here and continue to allow them in the validation?
or remove the numbers from the validation (but then i guess keep the string here as it) 😅

[nabramow]

@AndyMcGN Also remove them from the allowed characters in the validation!

We should probably also do that on backend too. Not sure if you're able to do backend? If not I will make a ticket for it.

[AndyMcGN]

sure, will take a look at the backend now

[nabramow]

Hey @AndyMcGN is this ready for review? Feel free to tag me when it is so I know!

[AndyMcGN]

@nabramow yes, this is ready for review, sorry for the delay! Added validation to backend too, see the pr below :)

[nabramow]

This looks good to me now! Let's make sure to merge this one before the backend one!

[github-actions]

📝 Release Notes

This PR should be included in the release notes.

Suggested release note:

Added display name validation during sign-up to prevent invalid names and show clearer error messages

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: include
Reasoning: This improves the signup flow by preventing invalid display names and giving clear feedback, which is a noticeable user-facing bug fix affecting new users creating accounts.