Asia/Calcutta frens

* Intl.DateTimeFormat().resolvedOptions().timeZone returns legacy TZ
  names, including Asia/Calcutta

* on Heroku we don't have tzdata-legacy package, thus the app cannot
  resolve this and other legacy TZs from user input

* mapping legacy TZs on frontend is expensive — additional code to ship
  to end-user

We could extend image builds with another buildpack, installing
tzdata-legacy package. We could also include gem, which works
immediately.

Read more:
https://hillenius.net/post/rangoon/
https://app.honeybadger.io/projects/58419/faults/117568048

Author: mostlyobvious

rails_application/Gemfile

@@ -32,4 +32,4 @@ end
 
 gem "infra", path: "../infra"
 
-gem "tzinfo-data", platforms: %i[mingw mswin x64_mingw jruby]
+gem "tzinfo-data"

rails_application/Gemfile.lock

@@ -331,6 +331,8 @@ GEM
       railties (>= 6.0.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
+    tzinfo-data (1.2025.2)
+      tzinfo (>= 1.0.0)
     unparser (0.8.0)
       diff-lcs (~> 1.6)
       parser (>= 3.3.0)