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/javascript/dashboard/components-next/AssignmentPolicy/AssignmentPolicyCard/AssignmentPolicyCard.story.vue

@@ -39,7 +39,6 @@ const policyA = withCount({
   description: 'Distributes conversations evenly among available agents',
   assignmentOrder: 'round_robin',
   conversationPriority: 'high',
-  enabled: true,
   inboxes: [mockInboxes[0], mockInboxes[1]],
   isFetchingInboxes: false,
 });
@@ -50,7 +49,6 @@ const policyB = withCount({
   description: 'Assigns based on capacity and workload',
   assignmentOrder: 'capacity_based',
   conversationPriority: 'medium',
-  enabled: true,
   inboxes: [mockInboxes[2], mockInboxes[3]],
   isFetchingInboxes: false,
 });
@@ -61,7 +59,6 @@ const emptyPolicy = withCount({
   description: 'Policy with no assigned inboxes',
   assignmentOrder: 'manual',
   conversationPriority: 'low',
-  enabled: false,
   inboxes: [],
   isFetchingInboxes: false,
 });

app/javascript/dashboard/components-next/AssignmentPolicy/AssignmentPolicyCard/AssignmentPolicyCard.vue

@@ -15,7 +15,6 @@ const props = defineProps({
   assignmentOrder: { type: String, default: '' },
   conversationPriority: { type: String, default: '' },
   assignedInboxCount: { type: Number, default: 0 },
-  enabled: { type: Boolean, default: false },
   inboxes: { type: Array, default: () => [] },
   isFetchingInboxes: { type: Boolean, default: false },
 });
@@ -65,22 +64,6 @@ const handleFetchInboxes = () => {
             {{ name }}
           </h3>
           <div class="flex items-center gap-2">
-            <div class="flex items-center rounded-md bg-n-alpha-2 h-6 px-2">
-              <span
-                class="text-xs"
-                :class="enabled ? 'text-n-teal-11' : 'text-n-slate-12'"
-              >
-                {{
-                  enabled
-                    ? t(
-                        'ASSIGNMENT_POLICY.AGENT_ASSIGNMENT_POLICY.INDEX.CARD.ACTIVE'
-                      )
-                    : t(
-                        'ASSIGNMENT_POLICY.AGENT_ASSIGNMENT_POLICY.INDEX.CARD.INACTIVE'
-                      )
-                }}
-              </span>
-            </div>
             <CardPopover
               :title="
                 t(