fix: V2 Assignment service enhancements (#13036)

## Linear Ticket:
https://linear.app/chatwoot/issue/CW-6081/review-feedback

## Description

Assignment V2 Service Enhancements

- Enable Assignment V2 on plan upgrade
- Fix UI issue with fair distribution policy display
- Add advanced assignment feature flag and enhance Assignment V2
capabilities

## Type of change

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

## How Has This Been Tested?

This has been tested using the UI.

## 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

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes auto-assignment execution paths, rate limiting defaults, and
feature-flag gating (including premium plan behavior), which could
affect which conversations get assigned and when. UI rewires inbox
settings and policy flows, so regressions are possible around
navigation/linking and feature visibility.
> 
> **Overview**
> **Adds a new premium `advanced_assignment` feature flag** and uses it
to gate capacity/balanced assignment features in the UI (sidebar entry,
settings routes, assignment-policy landing cards) and backend
(Enterprise balanced selector + capacity filtering).
`advanced_assignment` is marked premium, included in Business plan
entitlements, and auto-synced in Enterprise accounts when
`assignment_v2` is toggled.
> 
> **Improves Assignment V2 policy UX** by adding an inbox-level
“Conversation Assignment” section (behind `assignment_v2`) that can
link/unlink an assignment policy, navigate to create/edit policy flows
with `inboxId` query context, and show an inbox-link prompt after
creating a policy. The policy form now defaults to enabled, disables the
`balanced` option with a premium badge/message when unavailable, and
inbox lists support click-to-navigate.
> 
> **Tightens/adjusts auto-assignment behavior**: bulk assignment now
requires `inbox.enable_auto_assignment?`, conversation ordering uses the
attached `assignment_policy` priority, and rate limiting uses
`assignment_policy` config with an infinite default limit while still
tracking assignments. Tests and i18n strings are updated accordingly.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
23bc03bf75ee4376071e4d7fc7cd564c601d33d7. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Pranav <pranav@chatwoot.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/services/auto_assignment/assignment_service.rb

@@ -3,6 +3,7 @@ class AutoAssignment::AssignmentService
 
   def perform_bulk_assignment(limit: 100)
     return 0 unless inbox.auto_assignment_v2_enabled?
+    return 0 unless inbox.enable_auto_assignment?
 
     assigned_count = 0
 
@@ -32,7 +33,9 @@ class AutoAssignment::AssignmentService
   def unassigned_conversations(limit)
     scope = inbox.conversations.unassigned.open
 
-    scope = if assignment_config['conversation_priority'].to_s == 'longest_waiting'
+    # Apply conversation priority using assignment policy if available
+    policy = inbox.assignment_policy
+    scope = if policy&.longest_waiting?
               scope.reorder(last_activity_at: :asc, created_at: :asc)
             else
               scope.reorder(created_at: :asc)
@@ -81,10 +84,6 @@ class AutoAssignment::AssignmentService
   def round_robin_selector
     @round_robin_selector ||= AutoAssignment::RoundRobinSelector.new(inbox: inbox)
   end
-
-  def assignment_config
-    @assignment_config ||= inbox.auto_assignment_config || {}
-  end
 end
 
 AutoAssignment::AssignmentService.prepend_mod_with('AutoAssignment::AssignmentService')

app/services/auto_assignment/rate_limiter.rb

@@ -8,8 +8,6 @@ class AutoAssignment::RateLimiter
   end
 
   def track_assignment(conversation)
-    return unless enabled?
-
     assignment_key = build_assignment_key(conversation.id)
     Redis::Alfred.set(assignment_key, conversation.id.to_s, ex: window)
   end
@@ -24,11 +22,11 @@ class AutoAssignment::RateLimiter
   private
 
   def enabled?
-    limit.present? && limit.positive?
+    config.present? && limit.positive?
   end
 
   def limit
-    config&.fair_distribution_limit&.to_i || Math
+    config&.fair_distribution_limit.present? ? config.fair_distribution_limit.to_i : Float::INFINITY
   end
 
   def window