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/services/auto_assignment/assignment_service_spec.rb

@@ -10,8 +10,9 @@ RSpec.describe AutoAssignment::AssignmentService do
   let(:conversation) { create(:conversation, inbox: inbox, assignee: nil) }
 
   before do
-    # Enable assignment_v2 feature for the account
-    allow(account).to receive(:feature_enabled?).with('assignment_v2').and_return(true)
+    # Enable assignment_v2 feature for the account (basic assignment features)
+    account.enable_features('assignment_v2')
+    account.save!
     # Link inbox to assignment policy
     create(:inbox_assignment_policy, inbox: inbox, assignment_policy: assignment_policy)
     create(:inbox_member, inbox: inbox, user: agent)

spec/services/auto_assignment/rate_limiter_spec.rb

@@ -59,8 +59,9 @@ RSpec.describe AutoAssignment::RateLimiter do
         allow(inbox).to receive(:assignment_policy).and_return(nil)
       end
 
-      it 'does not track the assignment' do
-        expect(Redis::Alfred).not_to receive(:set)
+      it 'still tracks the assignment with default window' do
+        expected_key = format(Redis::RedisKeys::ASSIGNMENT_KEY, inbox_id: inbox.id, agent_id: agent.id, conversation_id: conversation.id)
+        expect(Redis::Alfred).to receive(:set).with(expected_key, conversation.id.to_s, ex: 24.hours.to_i)
         rate_limiter.track_assignment(conversation)
       end
     end