feat: Add a setting to keep conversations pending on bot failures (#13512)

Adds an account-level setting `keep_pending_on_bot_failure` to control
whether conversations should move from pending to open when agent bot
webhooks fail.

Some users experience occasional message drops and don't want
conversations to automatically reopen due to transient bot failures.
This setting gives accounts control over that behavior. This is a
temporary setting which will be removed in future once a proper fix for
it is done, so it is not added in the UI.

app/models/account.rb

@@ -40,6 +40,7 @@ class Account < ApplicationRecord
         'auto_resolve_ignore_waiting': { 'type': %w[boolean null] },
         'audio_transcriptions': { 'type': %w[boolean null] },
         'auto_resolve_label': { 'type': %w[string null] },
+        'keep_pending_on_bot_failure': { 'type': %w[boolean null] },
         'conversation_required_attributes': {
           'type': %w[array null],
           'items': { 'type': 'string' }
@@ -88,6 +89,7 @@ class Account < ApplicationRecord
 
   store_accessor :settings, :audio_transcriptions, :auto_resolve_label
   store_accessor :settings, :captain_models, :captain_features
+  store_accessor :settings, :keep_pending_on_bot_failure
 
   has_many :account_users, dependent: :destroy_async
   has_many :agent_bot_inboxes, dependent: :destroy_async