Reset Fields widget implementation (#19283)

## Context
This PR implements the first steps for overridable entities resets.

<img width="1277" height="568" alt="Screenshot 2026-04-02 at 18 58 04"
src="https://github.com/user-attachments/assets/4c7f93b1-c453-4905-a919-cd6af11e0e16"
/>

packages/twenty-server/src/engine/metadata-modules/flat-entity/utils/split-entities-by-reset-strategy.util.ts

@@ -0,0 +1,45 @@
+type EntityWithApplicationIdentifierAndOverrides = {
+  applicationUniversalIdentifier: string;
+  isActive: boolean;
+  overrides: unknown;
+};
+
+export const splitEntitiesByResetStrategy = <
+  T extends EntityWithApplicationIdentifierAndOverrides,
+>({
+  entities,
+  workspaceCustomApplicationUniversalIdentifier,
+  now,
+}: {
+  entities: T[];
+  workspaceCustomApplicationUniversalIdentifier: string;
+  now: string;
+}): {
+  toHardDelete: T[];
+  toReset: (T & { isActive: true; overrides: null; updatedAt: string })[];
+} => {
+  const toHardDelete: T[] = [];
+  const toReset: (T & {
+    isActive: true;
+    overrides: null;
+    updatedAt: string;
+  })[] = [];
+
+  for (const entity of entities) {
+    if (
+      entity.applicationUniversalIdentifier ===
+      workspaceCustomApplicationUniversalIdentifier
+    ) {
+      toHardDelete.push(entity);
+    } else {
+      toReset.push({
+        ...entity,
+        isActive: true as const,
+        overrides: null,
+        updatedAt: now,
+      });
+    }
+  }
+
+  return { toHardDelete, toReset };
+};