feat: 🎸 allow only active users to log in

[PeculiarE]

Fixes #1815

• PR is descriptively titled 📑 and links the original issue above 🔗
• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with rake test
• code is in uniquely-named feature branch and has no merge conflicts 📁
• screenshots/GIFs are attached 📎 in case of UI updation
• ask @publiclab/mapknitter-reviewers for help, in a comment below

[gitpod-io]

[codecov]

Codecov Report

Merging #1823 (75b0e7d) into main (3affa8b) will decrease coverage by 0.65%.
The diff coverage is 7.14%.

@@            Coverage Diff             @@
##             main    #1823      +/-   ##
==========================================
- Coverage   67.44%   66.79%   -0.66%     
==========================================
  Files          40       40              
  Lines        1321     1337      +16     
==========================================
+ Hits          891      893       +2     
- Misses        430      444      +14     

Impacted Files	Coverage Δ
app/controllers/sessions_controller.rb	29.34% <3.84%> (-3.99%)	⬇️
app/models/user.rb	97.36% <50.00%> (-2.64%)	⬇️