feat(workflow): expand manual-trigger runtime payload with payload + _metadata (#21676)

## Summary

Step 1 (**expand**) of restructuring the manual-trigger output so record
fields live under a `payload` key and trigger-level metadata (the
running workspace member) lives alongside it. This step is **additive
and runtime-only** — no behavior changes for existing workflows, and
nothing new is surfaced in the variable picker yet.

The manual-trigger runtime payload now additively carries:
- `payload`: a mirror of the incoming record fields, reachable at
`{{trigger.payload.*}}`
- `_metadata.workspaceMemberId`: the member who ran the workflow,
reachable at `{{trigger._metadata.workspaceMemberId}}`

Record fields are still served at the trigger root, so existing
`{{trigger.id}}` references keep working unchanged. The output schema /
variable picker is intentionally left untouched here.

### Why `_metadata` (underscore)
During the transition, record fields still sit at the `trigger` root
next to the injected keys. Field API names can't start with `_`, so
`_metadata` is collision-proof against any record field; picking the
name now avoids a later variable-path rename migration.

### Phasing
- **Step 1 (this PR):** write `payload` + `_metadata` at runtime; keep
using direct `trigger.*`; don't display the new paths.
- **Step 2:** surface `payload` + `_metadata` in the variable picker.
- **Step 3:** migrate existing variables to `trigger.payload.*` and
contract the root record fields.

## Test plan
- [x] `twenty-shared` builds, `twenty-server` typechecks, lint clean on
changed files
- [x] Manual: run a manually-triggered (SINGLE_RECORD) workflow and
confirm the run's trigger payload contains `payload.*` mirroring the
record and `_metadata.workspaceMemberId`
- [x] Manual: confirm existing `{{trigger.id}}` references still resolve

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packages/twenty-server/src/engine/core-modules/workflow/resolvers/workflow-trigger.resolver.ts

@@ -2,6 +2,11 @@ import { UseFilters, UseGuards, UsePipes } from '@nestjs/common';
 import { Args, Mutation } from '@nestjs/graphql';
 
 import { PermissionFlagType } from 'twenty-shared/constants';
+import {
+  WORKFLOW_TRIGGER_METADATA_KEY,
+  WORKFLOW_TRIGGER_METADATA_WORKSPACE_MEMBER_ID_KEY,
+  WORKFLOW_TRIGGER_PAYLOAD_KEY,
+} from 'twenty-shared/workflow';
 
 import { CoreResolver } from 'src/engine/api/graphql/graphql-config/decorators/core-resolver.decorator';
 import { UUIDScalarType } from 'src/engine/api/graphql/workspace-schema-builder/graphql-types/scalars';
@@ -98,7 +103,14 @@ export class WorkflowTriggerResolver {
     return this.workflowTriggerWorkspaceService.runWorkflowVersion({
       workflowVersionId,
       workflowRunId: workflowRunId ?? undefined,
-      payload: payload ?? {},
+      payload: {
+        ...(payload ?? {}),
+        [WORKFLOW_TRIGGER_PAYLOAD_KEY]: { ...(payload ?? {}) },
+        [WORKFLOW_TRIGGER_METADATA_KEY]: {
+          [WORKFLOW_TRIGGER_METADATA_WORKSPACE_MEMBER_ID_KEY]:
+            workspaceMember.id,
+        },
+      },
       createdBy: buildCreatedByFromFullNameMetadata({
         fullNameMetadata: {
           firstName: workspaceMember.name.firstName,