fix: prevent NoMethodError in mute helpers when contact is nil (#13277)

## Linear Ticket

https://linear.app/chatwoot/issue/CW-4569/nomethoderror-undefined-method-blocked-for-nil-nomethoderror

## Description
Fixes NoMethodError in ConversationMuteHelpers that occurs during
contact deletion race condition.
When a contact is deleted, there's a brief window (~50-150ms) where
contact_id becomes nil but conversations still exist. If ResolutionJob
runs during this window, the muted? method crashes trying to call
blocked? on nil.Fixes # (issue)

## Type of change

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

## How Has This Been Tested?

- Created orphaned conversations (contact_id = nil)
- Called muted?, mute!, unmute! - all return gracefully
- Verified async deletion still works correctly

## 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



Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/jobs/conversations/resolution_job.rb

@@ -16,10 +16,12 @@ class Conversations::ResolutionJob < ApplicationJob
   private
 
   def conversation_scope(account)
-    if account.auto_resolve_ignore_waiting
-      account.conversations.resolvable_not_waiting(account.auto_resolve_after)
-    else
-      account.conversations.resolvable_all(account.auto_resolve_after)
-    end
+    base_scope = if account.auto_resolve_ignore_waiting
+                   account.conversations.resolvable_not_waiting(account.auto_resolve_after)
+                 else
+                   account.conversations.resolvable_all(account.auto_resolve_after)
+                 end
+    # Exclude orphan conversations where contact was deleted but conversation cleanup is pending
+    base_scope.where.not(contact_id: nil)
   end
 end

app/models/concerns/conversation_mute_helpers.rb

@@ -2,17 +2,21 @@ module ConversationMuteHelpers
   extend ActiveSupport::Concern
 
   def mute!
+    return unless contact
+
     resolved!
     contact.update(blocked: true)
     create_muted_message
   end
 
   def unmute!
+    return unless contact
+
     contact.update(blocked: false)
     create_unmuted_message
   end
 
   def muted?
-    contact.blocked?
+    contact&.blocked? || false
   end
 end