General close reason fixes and improvements

[Oaphi]

This PR is primarily concerned with properly scoping close reasons for non-global admins.

Additional minor changes:

• ostruct is now an explicit dependency. No functional changes, just fixes the warning spam that'll eventually turn into an error:

  /code/config/initializers/config.rb:1: warning: ostruct was loaded from the standard library
  , but will no longer be part of the default gems starting from Ruby 3.5.0.
  You can add ostruct to your Gemfile or gemspec to silence this warning.

• allows abilities to be updated network-wide even if their descriptions differ - the original restriction breaks multi-community tests. The original restriction was put there by me when implementing the feature out of caution - at this point I am sure it's safe to remove it.
• identical_post_spam no longer triggers on posts seeded by the system user;

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.40%. Comparing base (9e3f230) to head (1d9e6b6).

Additional details and impacted files

Components	Coverage Δ
controllers	77.07% <100.00%> (+0.01%)	⬆️
helpers	85.47% <ø> (ø)
jobs	79.93% <ø> (ø)
models	93.50% <100.00%> (+0.02%)	⬆️
tasks	61.11% <ø> (ø)
scripts	∅ <ø> (∅)

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