Use new auto-generated client API in frontend admin interface

[lkeegan]

• remove api logic from admin.ts
• simplify preview of uploaded images
• add localised translations for more text elements
• add localised alert message for invalid login attempt
• fix inconsistent name of delete_user_question admin endpoint
• don't generate separate Input and Output types in client API
  • by passing separate_input_output_schemas=False to get_openapi call

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0.90498% with 219 lines in your changes missing coverage. Please review.

Project coverage is 14.97%. Comparing base (aeb25ce) to head (c3382dc).

Files with missing lines	Patch %	Lines
...nd/src/lib/components/Admin/MilestoneGroups.svelte	0.00%	64 Missing ⚠️
...ib/components/Admin/EditMilestoneGroupModal.svelte	0.00%	42 Missing ⚠️
...src/lib/components/Admin/EditMilestoneModal.svelte	0.00%	34 Missing ⚠️
...tend/src/lib/components/Admin/UserQuestions.svelte	0.00%	23 Missing ⚠️
.../lib/components/Admin/EditUserQuestionModal.svelte	0.00%	22 Missing ⚠️
frontend/src/lib/admin.ts	0.00%	11 Missing ⚠️
frontend/src/lib/components/Admin/Login.svelte	0.00%	9 Missing ⚠️
frontend/src/lib/components/Admin/Languages.svelte	0.00%	4 Missing ⚠️
frontend/src/lib/client/services.gen.ts	0.00%	3 Missing ⚠️
frontend/src/lib/stores/adminStore.ts	0.00%	2 Missing ⚠️
... and 5 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #100      +/-   ##
==========================================
+ Coverage   14.15%   14.97%   +0.81%     
==========================================
  Files          90       90              
  Lines        5064     4789     -275     
  Branches      118      118              
==========================================
  Hits          717      717              
+ Misses       4284     4009     -275     
  Partials       63       63              

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[sonarqubecloud]

Quality Gate failed

Failed conditions
E Reliability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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