476 small UI changes

[jmsssc]

• Change the appearance of the guest account user hint to register.
• Change the milestone groups page to nolonger show buttons.

Milestone groups checkboxes are removed. Disabled milestone groups (meaning no milestones within a milestone group) are still hidden.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.44%. Comparing base (bdedb31) to head (e013ecb).

Files with missing lines	Patch %	Lines
frontend/src/routes/userLand/+layout.svelte	0.00%	3 Missing ⚠️
...d/src/routes/userLand/milestone/group/+page.svelte	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #485   +/-   ##
=======================================
  Coverage   26.44%   26.44%           
=======================================
  Files         149      149           
  Lines        7910     7910           
  Branches      108      108           
=======================================
  Hits         2092     2092           
  Misses       5807     5807           
  Partials       11       11           

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