unify layout between auth pages

[noerw]

Several auth pages had plenty of differences in container width, style for tabs / menu, text alignment. This is now all unified.
Also fixes a broken form layout on /user/link_account page on large screens.

This makes changes to the templates, but should be compatible to the old structure (I made sure to keep the important classes)

page	this PR	v1.13.0-rc1
sign up
sign in
link account

[codecov-io]

Codecov Report

Merging #13547 (d9e2212) into master (6280af0) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #13547      +/-   ##
==========================================
- Coverage   42.17%   42.16%   -0.02%     
==========================================
  Files         696      696              
  Lines       76438    76438              
==========================================
- Hits        32241    32232       -9     
- Misses      38911    38920       +9     
  Partials     5286     5286              

Impacted Files	Coverage Δ
services/pull/temp_repo.go	26.59% <0.00%> (-3.20%)	⬇️
services/pull/check.go	48.90% <0.00%> (-2.92%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
services/pull/patch.go	53.97% <0.00%> (-1.71%)	⬇️
modules/queue/workerpool.go	58.77% <0.00%> (-1.23%)	⬇️
modules/queue/unique_queue_disk_channel.go	55.38% <0.00%> (+1.53%)	⬆️
modules/charset/charset.go	73.03% <0.00%> (+4.49%)	⬆️

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