Access user account info from nav

[rossta]

Implement dialog to display user account info.

User sessions are still behind a feature flag, but this PR takes a first step toward providing a basic session dialog.

[codecov]

Codecov Report

Attention: Patch coverage is 77.22222% with 41 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
app/views/components/forms/stack.rb	0.00%	39 Missing ⚠️
app/views/users/confirmations/new_view.rb	0.00%	1 Missing ⚠️
app/views/users/header_navigations/show_view.rb	97.91%	1 Missing ⚠️

Files with missing lines	Coverage Δ
app/controllers/concerns/authentication.rb	100.00% <100.00%> (ø)
...controllers/users/header_navigations_controller.rb	100.00% <100.00%> (ø)
app/models/gravatar.rb	100.00% <100.00%> (ø)
app/models/guest.rb	100.00% <100.00%> (ø)
app/models/user.rb	97.95% <100.00%> (+0.18%)	⬆️
app/views/components/dark_mode/switch.rb	100.00% <100.00%> (ø)
app/views/components/dialog/layout.rb	100.00% <100.00%> (ø)
app/views/components/front_door/form.rb	100.00% <100.00%> (ø)
app/views/components/site_header/header.rb	100.00% <100.00%> (ø)
app/views/components/site_header/nav.rb	100.00% <100.00%> (ø)
... and 14 more