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/jobs/inboxes/fetch_imap_email_inboxes_job.rb

@@ -15,6 +15,7 @@ class Inboxes::FetchImapEmailInboxesJob < ApplicationJob
     return false if inbox.account.suspended?
     return false unless inbox.channel.imap_enabled
     return false if inbox.channel.reauthorization_required?
+    return false if inbox.channel.in_backoff?
 
     return true unless ChatwootApp.chatwoot_cloud?
     return false if default_plan?(inbox.account)

app/jobs/inboxes/fetch_imap_emails_job.rb

@@ -6,26 +6,29 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
   def perform(channel, interval = 1)
     return unless should_fetch_email?(channel)
 
-    key = format(::Redis::Alfred::EMAIL_MESSAGE_MUTEX, inbox_id: channel.inbox.id)
-
-    with_lock(key, 5.minutes) do
-      process_email_for_channel(channel, interval)
-    end
-  rescue *ExceptionList::IMAP_EXCEPTIONS => e
-    Rails.logger.error "Authorization error for email channel - #{channel.inbox.id} : #{e.message}"
-  rescue EOFError, OpenSSL::SSL::SSLError, Net::IMAP::NoResponseError, Net::IMAP::BadResponseError, Net::IMAP::InvalidResponseError,
-         Net::IMAP::ResponseParseError, Net::IMAP::ResponseReadError, Net::IMAP::ResponseTooLargeError => e
-    Rails.logger.error "Error for email channel - #{channel.inbox.id} : #{e.message}"
-  rescue LockAcquisitionError
-    Rails.logger.error "Lock failed for #{channel.inbox.id}"
+    fetch_emails_with_backoff(channel, interval)
   rescue StandardError => e
     ChatwootExceptionTracker.new(e, account: channel.account).capture_exception
   end
 
   private
 
+  def fetch_emails_with_backoff(channel, interval)
+    key = format(::Redis::Alfred::EMAIL_MESSAGE_MUTEX, inbox_id: channel.inbox.id)
+    with_lock(key, 5.minutes) { process_email_for_channel(channel, interval) }
+    channel.clear_backoff!
+  rescue Imap::AuthenticationError => e
+    Rails.logger.error "#{channel.backoff_log_identifier} authentication error : #{e.message}"
+    channel.authorization_error!
+  rescue *ExceptionList::IMAP_TRANSIENT_EXCEPTIONS => e
+    Rails.logger.error "#{channel.backoff_log_identifier} transient error : #{e.message}"
+    channel.apply_backoff!
+  rescue LockAcquisitionError
+    Rails.logger.error "Lock failed for #{channel.inbox.id}"
+  end
+
   def should_fetch_email?(channel)
-    channel.imap_enabled? && !channel.reauthorization_required?
+    channel.imap_enabled? && !channel.reauthorization_required? && !channel.in_backoff?
   end
 
   def process_email_for_channel(channel, interval)