fix: add explicit remove assignment actions to macros and automations (#12172)

This updates macros and automations so agents can explicitly remove
assigned agents or teams, while keeping the existing `Assign -> None`
flow working for backward compatibility.

Fixes: #7551
Closes: #7551

## Why
The original macro change exposed unassignment only through `Assign ->
None`, which made macros behave differently from automations and left
the explicit remove actions inconsistent across the product. This keeps
the lower-risk compatibility path and adds the explicit remove actions
requested in review.

## What this change does
- Adds `Remove Assigned Agent` and `Remove Assigned Team` as explicit
actions in macros.
- Adds the same explicit remove actions in automations.
- Keeps `Assign Agent -> None` and `Assign Team -> None` working for
existing behavior and stored payloads.
- Preserves backward compatibility for existing macro and automation
execution payloads.
- Downmerges the latest `develop` and resolves the conflicts while
keeping both the new remove actions and current `develop` behavior.

## Validation
- Verified both remove actions are available and selectable in the macro
editor.
- Verified both remove actions are available and selectable in the
automation builder.
- Applied a disposable macro with `Remove Assigned Agent` and `Remove
Assigned Team` on a real conversation and confirmed both fields were
cleared.
- Applied a disposable macro with `Assign Agent -> None` and `Assign
Team -> None` on a real conversation and confirmed both fields were
still cleared.

app/javascript/dashboard/composables/useMacros.js

@@ -15,6 +15,11 @@ export const useMacros = () => {
   const teams = computed(() => getters['teams/getTeams'].value);
   const agents = computed(() => getters['agents/getVerifiedAgents'].value);
 
+  const withNoneOption = options => [
+    { id: 'nil', name: t('AUTOMATION.NONE_OPTION') },
+    ...(options || []),
+  ];
+
   /**
    * Get dropdown values based on the specified type
    * @param {string} type - The type of dropdown values to retrieve
@@ -23,10 +28,15 @@ export const useMacros = () => {
   const getMacroDropdownValues = type => {
     switch (type) {
       case 'assign_team':
+        return withNoneOption(teams.value);
       case 'send_email_to_team':
         return teams.value;
       case 'assign_agent':
-        return [{ id: 'self', name: 'Self' }, ...agents.value];
+        return [
+          ...withNoneOption(),
+          { id: 'self', name: 'Self' },
+          ...agents.value,
+        ];
       case 'add_label':
       case 'remove_label':
         return labels.value.map(i => ({