fix: call authorization_error! on IMAP auth failures (#13560)

## Notion document

https://www.notion.so/chatwoot/Email-IMAP-Issue-30aa5f274c928062aa6bddc2e5877a63?showMoveTo=true&saveParent=true

## Description

PLAIN IMAP channels (non-OAuth) were silently retrying failed
authentication every minute, forever. When credentials are
wrong/expired, Net::IMAP::NoResponseError was caught and logged but
channel.authorization_error! was never called — so the Redis error
counter never incremented, reauthorization_required? was never set, and
admins were never notified. OAuth channels already had this handled
correctly via the Reauthorizable concern.
Additionally, Net::IMAP::ResponseParseError (raised by non-RFC-compliant
IMAP servers) was falling through to the StandardError catch-all,
flooding
Estimated impact before fix: ~70–75 broken IMAP inboxes generating
~700k–750k wasted Sidekiq jobs/week.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/models/concerns/reauthorizable.rb

@@ -13,6 +13,8 @@
 module Reauthorizable
   extend ActiveSupport::Concern
 
+  include Backoffable
+
   AUTHORIZATION_ERROR_THRESHOLD = 2
 
   # model attribute
@@ -65,6 +67,7 @@ module Reauthorizable
   def reauthorized!
     ::Redis::Alfred.delete(authorization_error_count_key)
     ::Redis::Alfred.delete(reauthorization_required_key)
+    clear_backoff!
 
     invalidate_inbox_cache unless instance_of?(::AutomationRule)
   end