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/helper/specs/macrosHelper.spec.js

@@ -45,6 +45,10 @@ describe('#resolveTeamIds', () => {
     const resolvedTeams = '⚙️ sales team, 🤷‍♂️ fayaz';
     expect(resolveTeamIds(teams, [1, 2])).toEqual(resolvedTeams);
   });
+
+  it('resolves nil as None', () => {
+    expect(resolveTeamIds(teams, ['nil'])).toEqual('None');
+  });
 });
 
 describe('#resolveLabels', () => {
@@ -59,6 +63,10 @@ describe('#resolveAgents', () => {
     const resolvedAgents = 'John Doe';
     expect(resolveAgents(agents, [1])).toEqual(resolvedAgents);
   });
+
+  it('resolves nil and self values', () => {
+    expect(resolveAgents(agents, ['nil', 'self'])).toEqual('None, Self');
+  });
 });
 
 describe('#getFileName', () => {