[PUI] Add startpage to admin

[matmair]

This PR adds a "start page" to the Admin Center.

• Global home button that stays afloat
• Adds (functioning) quick actions
• Adds server status on start page
• General info what the admin center is meant to be

Closes invenhost#108
Closes invenhost#112
Closes invenhost#113

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[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.

Project coverage is 83.48%. Comparing base (d1c8354) to head (4e7fca7).

Files	Patch %	Lines
...c/frontend/src/components/settings/QuickAction.tsx	71.42%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7995      +/-   ##
==========================================
- Coverage   83.57%   83.48%   -0.09%     
==========================================
  Files        1140     1133       -7     
  Lines       51013    50420     -593     
  Branches     1774     1765       -9     
==========================================
- Hits        42633    42094     -539     
+ Misses       7925     7869      -56     
- Partials      455      457       +2     

Flag	Coverage Δ
pui	65.57% <85.18%> (+0.40%)	⬆️

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