[FRONT COMPONENTS] Headless components (#18096)

## Description

- Add `isHeadless` field to `FrontComponent` entity so front components
can run without rendering UI in the command menu
- Introduce headless front component mounting logic:
`HeadlessFrontComponentMountRoot` at the application root,
`useMountHeadlessFrontComponent`, and `useUnmountHeadlessFrontComponent`
hooks to mount/unmount headless components
- Expand the SDK with new action components (`Action`, `ActionLink`,
`ActionOpenSidePanelPage`) and host communication functions
(`openSidePanelPage`, `unmountFrontComponent`)
- Move `CommandMenuPages` type to twenty-shared so the SDK can reference
it for side panel navigation

## Video QA



https://github.com/user-attachments/assets/4f9e3bb1-fcd1-42be-b3f4-a97e80c2add2

packages/twenty-front/src/modules/front-components/hooks/useUnmountHeadlessFrontComponent.ts

@@ -0,0 +1,19 @@
+import { useRecoilCallback } from 'recoil';
+
+import { mountedHeadlessFrontComponentIdsState } from '@/front-components/states/mountedHeadlessFrontComponentIdsState';
+
+export const useUnmountHeadlessFrontComponent = () => {
+  const unmountHeadlessFrontComponent = useRecoilCallback(
+    ({ set }) =>
+      (frontComponentId: string) => {
+        set(mountedHeadlessFrontComponentIdsState, (previousIds) => {
+          const next = new Set(previousIds);
+          next.delete(frontComponentId);
+          return next;
+        });
+      },
+    [],
+  );
+
+  return unmountHeadlessFrontComponent;
+};