feat: allow zero conversation limit capacity policy (#13964)

## Description

Two improvements to Agent Capacity Policy:

**1. Support exclusion via zero conversation limit**
Allow `conversation_limit` to be `0` on inbox capacity limits. Agents
with a zero limit are excluded from auto-assignment for that inbox while
remaining members for manual assignment.

**2. Fix exclusion rules duration input**
- Default changed from `10` to `null` so time-based exclusion isn't
applied unless explicitly set.
- Minimum lowered from 10 to 1 minute.
- `DurationInput` updated to handle `null` values correctly.

## Type of change

Please delete options that are not relevant.

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- Added model and capacity service specs for zero-limit exclusion
behavior.
- Tested manually via UI flows 

## 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

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

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

@@ -20,11 +20,11 @@ const excludedLabels = defineModel('excludedLabels', {
 
 const excludeOlderThanMinutes = defineModel('excludeOlderThanMinutes', {
   type: Number,
-  default: 10,
+  default: null,
 });
 
-// Duration limits: 10 minutes to 999 days (in minutes)
-const MIN_DURATION_MINUTES = 10;
+// Duration limits: 1 minute to 999 days (in minutes)
+const MIN_DURATION_MINUTES = 1;
 const MAX_DURATION_MINUTES = 1438560; // 999 days * 24 hours * 60 minutes
 
 const { t } = useI18n();

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

@@ -27,7 +27,7 @@ const { t } = useI18n();
 
 const BASE_KEY = 'ASSIGNMENT_POLICY.AGENT_CAPACITY_POLICY';
 const DEFAULT_CONVERSATION_LIMIT = 10;
-const MIN_CONVERSATION_LIMIT = 1;
+const MIN_CONVERSATION_LIMIT = 0;
 const MAX_CONVERSATION_LIMIT = 100000;
 
 const selectedInboxIds = computed(
@@ -42,6 +42,7 @@ const availableInboxes = computed(() =>
 
 const isLimitValid = limit => {
   return (
+    Number.isInteger(limit.conversationLimit) &&
     limit.conversationLimit >= MIN_CONVERSATION_LIMIT &&
     limit.conversationLimit <= MAX_CONVERSATION_LIMIT
   );

app/javascript/dashboard/components-next/input/DurationInput.vue

@@ -32,6 +32,7 @@ const convertToMinutes = newValue => {
 
 const transformedValue = computed({
   get() {
+    if (duration.value == null) return null;
     if (unit.value === DURATION_UNITS.MINUTES) return duration.value;
     if (unit.value === DURATION_UNITS.HOURS)
       return Math.floor(duration.value / 60);
@@ -41,6 +42,10 @@ const transformedValue = computed({
     return 0;
   },
   set(newValue) {
+    if (newValue == null || newValue === '') {
+      duration.value = null;
+      return;
+    }
     let minuteValue = convertToMinutes(newValue);
 
     duration.value = Math.min(Math.max(minuteValue, props.min), props.max);
@@ -53,6 +58,7 @@ const transformedValue = computed({
 // this might create some confusion, especially when saving
 // this watcher fixes it by rounding the duration basically, to the nearest unit value
 watch(unit, () => {
+  if (duration.value == null) return;
   let adjustedValue = convertToMinutes(transformedValue.value);
   duration.value = Math.min(Math.max(adjustedValue, props.min), props.max);
 });

app/javascript/dashboard/routes/dashboard/settings/assignmentPolicy/pages/AgentCapacityEditPage.vue

@@ -81,7 +81,7 @@ const formData = computed(() => ({
       ...(selectedPolicy.value?.exclusionRules?.excludedLabels || []),
     ],
     excludeOlderThanHours:
-      selectedPolicy.value?.exclusionRules?.excludeOlderThanHours || 10,
+      selectedPolicy.value?.exclusionRules?.excludeOlderThanHours ?? null,
   },
   inboxCapacityLimits:
     selectedPolicy.value?.inboxCapacityLimits?.map(limit => ({

app/javascript/dashboard/routes/dashboard/settings/assignmentPolicy/pages/components/AgentCapacityPolicyForm.vue

@@ -17,7 +17,7 @@ const props = defineProps({
       enabled: false,
       exclusionRules: {
         excludedLabels: [],
-        excludeOlderThanHours: 10,
+        excludeOlderThanHours: null,
       },
       inboxCapacityLimits: [],
     }),
@@ -84,7 +84,7 @@ const state = reactive({
   description: '',
   exclusionRules: {
     excludedLabels: [],
-    excludeOlderThanHours: 10,
+    excludeOlderThanHours: null,
   },
   inboxCapacityLimits: [],
 });
@@ -120,7 +120,7 @@ const resetForm = () => {
     description: '',
     exclusionRules: {
       excludedLabels: [],
-      excludeOlderThanHours: 10,
+      excludeOlderThanHours: null,
     },
     inboxCapacityLimits: [],
   });