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/components/FairDistribution.vue

@@ -1,5 +1,5 @@
 <script setup>
-import { ref, onMounted } from 'vue';
+import { ref, computed, onMounted } from 'vue';
 import { useI18n } from 'vue-i18n';
 import Input from 'dashboard/components-next/input/Input.vue';
 import DurationInput from 'dashboard/components-next/input/DurationInput.vue';
@@ -15,6 +15,9 @@ const fairDistributionLimit = defineModel('fairDistributionLimit', {
   },
 });
 
+// The model value is in seconds (for the backend/DB)
+// DurationInput works in minutes internally
+// We need to convert between seconds and minutes
 const fairDistributionWindow = defineModel('fairDistributionWindow', {
   type: Number,
   default: 3600,
@@ -25,6 +28,17 @@ const fairDistributionWindow = defineModel('fairDistributionWindow', {
 
 const windowUnit = ref(DURATION_UNITS.MINUTES);
 
+// Convert seconds to minutes for DurationInput
+const windowInMinutes = computed({
+  get() {
+    return Math.floor((fairDistributionWindow.value || 0) / 60);
+  },
+  set(minutes) {
+    fairDistributionWindow.value = minutes * 60;
+  },
+});
+
+// Detect unit based on minutes (converted from seconds)
 const detectUnit = minutes => {
   const m = Number(minutes) || 0;
   if (m === 0) return DURATION_UNITS.MINUTES;
@@ -34,7 +48,7 @@ const detectUnit = minutes => {
 };
 
 onMounted(() => {
-  windowUnit.value = detectUnit(fairDistributionWindow.value);
+  windowUnit.value = detectUnit(windowInMinutes.value);
 });
 </script>
 
@@ -73,9 +87,9 @@ onMounted(() => {
       <div
         class="flex items-center gap-2 flex-1 [&>select]:!bg-n-alpha-2 [&>select]:!outline-none [&>select]:hover:brightness-110"
       >
-        <!-- allow 10 mins to 999 days -->
+        <!-- allow 10 mins to 999 days (in minutes) -->
         <DurationInput
-          v-model:model-value="fairDistributionWindow"
+          v-model:model-value="windowInMinutes"
           v-model:unit="windowUnit"
           :min="10"
           :max="1438560"