Per request, a display name is now mandatory when signing up:
- Removed the "Skip for now" button from the profile step — the only forward
path is Save, which is disabled until a non-empty name is entered.
- Marked the field required (*), added helper copy ("Required — how you'll show
up across SkateSpots. Change it anytime."), and a hint under the button.
- finishSignup guards against an empty/whitespace name (defense-in-depth for
keyboard/Enter), trims the name before publishing kind 0.
- Reworded the step copy: name required, bio + avatar still optional.
Only affects the primary nsec signup dialog (also the endpoint the mnemonic
flow feeds into); the mnemonic dialog has no name step.
Co-authored-by: shakespeare.diy <assistant@shakespeare.diy>
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