fix(workflow): add tooltip explaining why the variable picker is disabled (#21862)

## Context

Closes #21773
<img width="448" height="301" alt="Capture d’écran 2026-06-19 à 16 33
56"
src="https://github.com/user-attachments/assets/4efc637e-3361-4108-86b6-92ffc2e84252"
/>


When a workflow's variable picker (the `+` button next to a field) is
disabled — e.g. on a step whose only trigger is a global manual trigger
that produces no record variables — the button just shows a
`not-allowed` cursor with no explanation of *why*.

## Change

Add an `AppTooltip` to the disabled state of `WorkflowVariablesDropdown`
explaining the reason:

> No variables are available yet. Variables come from the workflow
trigger and previous steps.

The disabled state is reached via `disabled === true ||
noAvailableVariables`. In practice the callers hide the picker entirely
in read-only mode (it's rendered only when `!disabled`/`!readonly`), so
the meaningful trigger is **no available variables** — hence a single
message rather than separate copy per reason.

The tooltip is anchored with a `data-*` attribute selector instead of an
`#id`, because the picker's `instanceId` comes from React's `useId()`
(values like `:r1:`) which are invalid in a CSS `#id` selector that
`AppTooltip` runs through `querySelectorAll`.

## Testing

- `nx lint:diff-with-main twenty-front` — passes (lint + format).
- Verified the component resolves/renders on a local instance running
this branch.

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packages/twenty-front/src/modules/workflow/workflow-variables/components/WorkflowVariablesDropdown.tsx

@@ -7,10 +7,12 @@ import { type InputSchemaPropertyType } from 'twenty-shared/workflow';
 
 import { useAvailableVariablesInWorkflowStep } from '@/workflow/workflow-variables/hooks/useAvailableVariablesInWorkflowStep';
 import { type StepOutputSchemaV2 } from '@/workflow/workflow-variables/types/StepOutputSchemaV2';
+import { t } from '@lingui/core/macro';
 import { styled } from '@linaria/react';
 import { useContext, useState } from 'react';
 import { isDefined } from 'twenty-shared/utils';
 import { IconVariablePlus } from 'twenty-ui/icon';
+import { AppTooltip, TooltipDelay, TooltipPosition } from 'twenty-ui/surfaces';
 import { ThemeContext, themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledDropdownVariableButtonContainer = styled.div<{
@@ -85,12 +87,25 @@ export const WorkflowVariablesDropdown = ({
 
   if (disabled === true || noAvailableVariables) {
     return (
-      <StyledDropdownVariableButtonContainer disabled={true}>
-        <IconVariablePlus
-          size={theme.icon.size.md}
-          color={theme.font.color.light}
+      <>
+        <StyledDropdownVariableButtonContainer
+          disabled={true}
+          data-variable-picker-disabled-anchor={dropdownId}
+        >
+          <IconVariablePlus
+            size={theme.icon.size.md}
+            color={theme.font.color.light}
+          />
+        </StyledDropdownVariableButtonContainer>
+        <AppTooltip
+          anchorSelect={`[data-variable-picker-disabled-anchor="${dropdownId}"]`}
+          content={t`No variables are available yet. Variables come from the workflow trigger and previous steps.`}
+          place={TooltipPosition.Top}
+          delay={TooltipDelay.mediumDelay}
+          offset={5}
+          noArrow
         />
-      </StyledDropdownVariableButtonContainer>
+      </>
     );
   }