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>

spec/jobs/auto_assignment/periodic_assignment_job_spec.rb

@@ -14,13 +14,13 @@ RSpec.describe AutoAssignment::PeriodicAssignmentJob, type: :job do
   describe '#perform' do
     context 'when account has assignment_v2 feature enabled' do
       before do
-        allow(account).to receive(:feature_enabled?).with('assignment_v2').and_return(true)
+        account.enable_features('assignment_v2')
+        account.save!
         allow(Account).to receive(:find_in_batches).and_yield([account])
       end
 
-      context 'when inbox has auto_assignment_v2 enabled' do
+      context 'when inbox has assignment policy or auto assignment enabled' do
         before do
-          allow(inbox).to receive(:auto_assignment_v2_enabled?).and_return(true)
           inbox_relation = instance_double(ActiveRecord::Relation)
           allow(account).to receive(:inboxes).and_return(inbox_relation)
           allow(inbox_relation).to receive(:joins).with(:assignment_policy).and_return(inbox_relation)
@@ -41,8 +41,8 @@ RSpec.describe AutoAssignment::PeriodicAssignmentJob, type: :job do
           policy2 = create(:assignment_policy, account: account2)
           create(:inbox_assignment_policy, inbox: inbox2, assignment_policy: policy2)
 
-          allow(account2).to receive(:feature_enabled?).with('assignment_v2').and_return(true)
-          allow(inbox2).to receive(:auto_assignment_v2_enabled?).and_return(true)
+          account2.enable_features('assignment_v2')
+          account2.save!
 
           inbox_relation2 = instance_double(ActiveRecord::Relation)
           allow(account2).to receive(:inboxes).and_return(inbox_relation2)
@@ -58,9 +58,10 @@ RSpec.describe AutoAssignment::PeriodicAssignmentJob, type: :job do
         end
       end
 
-      context 'when inbox does not have auto_assignment_v2 enabled' do
+      context 'when inbox does not have assignment policy or auto assignment enabled' do
         before do
-          allow(inbox).to receive(:auto_assignment_v2_enabled?).and_return(false)
+          inbox.update!(enable_auto_assignment: false)
+          InboxAssignmentPolicy.where(inbox: inbox).destroy_all
         end
 
         it 'does not queue assignment job' do
@@ -73,7 +74,6 @@ RSpec.describe AutoAssignment::PeriodicAssignmentJob, type: :job do
 
     context 'when account does not have assignment_v2 feature enabled' do
       before do
-        allow(account).to receive(:feature_enabled?).with('assignment_v2').and_return(false)
         allow(Account).to receive(:find_in_batches).and_yield([account])
       end
 
@@ -90,11 +90,11 @@ RSpec.describe AutoAssignment::PeriodicAssignmentJob, type: :job do
         # Create multiple accounts
         5.times do |_i|
           acc = create(:account)
+          acc.enable_features('assignment_v2')
+          acc.save!
           inb = create(:inbox, account: acc, enable_auto_assignment: true)
           policy = create(:assignment_policy, account: acc)
           create(:inbox_assignment_policy, inbox: inb, assignment_policy: policy)
-          allow(acc).to receive(:feature_enabled?).with('assignment_v2').and_return(true)
-          allow(inb).to receive(:auto_assignment_v2_enabled?).and_return(true)
 
           inbox_relation = instance_double(ActiveRecord::Relation)
           allow(acc).to receive(:inboxes).and_return(inbox_relation)