feat: sync calendar instantly on changes

[st3iny]

This approach requires notify_push.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.

Project coverage is 29.18%. Comparing base (bd73f27) to head (97948db).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/store/calendars.js	0.00%	16 Missing and 2 partials ⚠️
src/services/notifyService.js	0.00%	10 Missing and 1 partial ⚠️
src/views/Calendar.vue	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6364      +/-   ##
============================================
+ Coverage     23.54%   29.18%   +5.63%     
- Complexity      454      916     +462     
============================================
  Files           247      291      +44     
  Lines         11700    13988    +2288     
  Branches       2203     2204       +1     
============================================
+ Hits           2755     4082    +1327     
- Misses         8625     9583     +958     
- Partials        320      323       +3     

Flag	Coverage Δ
javascript	15.05% <0.00%> (-0.03%)	⬇️
php	58.97% <ø> (-0.56%)	⬇️

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[tcitworld]

This is nice, but I feel working with Sabre's DAV Push to use WebPush would be half the work and bring the same functionality to 3rd-party clients for the same cost?