feat: support whitelabelling in the embedding (#1491)

## Description

Adds support for customising the theme and CSS for the embedding
components which is restricted to platform customers and above.

Additionally adds proper support for the platform plan which will let us
update our stripe products.

<img width="1040" alt="image"
src="https://github.com/user-attachments/assets/f694cd1e-ac93-4dc0-9f78-92fa813f6404">
<img width="1015" alt="image"
src="https://github.com/user-attachments/assets/4209972a-b2bd-40c9-9049-0367382a4de5">
<img width="1065" alt="image"
src="https://github.com/user-attachments/assets/fdbaaaa5-a028-4b1d-a58a-ea6224e21abe">


## Related Issue

N/A

## Changes Made

- Added support for using CSS Vars and CSS within the embedding route
- Added a guard for platform and enterprise plans to activate the custom
css
- Added support for the platform plan

## Testing Performed
Yes

apps/web/src/app/embed/sign/[[...url]]/client.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useEffect, useState } from 'react';
+import { useEffect, useLayoutEffect, useState } from 'react';
 
 import { Trans, msg } from '@lingui/macro';
 import { useLingui } from '@lingui/react';
@@ -28,6 +28,7 @@ import { Logo } from '~/components/branding/logo';
 import { EmbedClientLoading } from '../../client-loading';
 import { EmbedDocumentCompleted } from '../../completed';
 import { EmbedDocumentFields } from '../../document-fields';
+import { injectCss } from '../../util';
 import { ZSignDocumentEmbedDataSchema } from './schema';
 
 export type EmbedSignDocumentClientPageProps = {
@@ -38,6 +39,8 @@ export type EmbedSignDocumentClientPageProps = {
   fields: Field[];
   metadata?: DocumentMeta | TemplateMeta | null;
   isCompleted?: boolean;
+  hidePoweredBy?: boolean;
+  isPlatformOrEnterprise?: boolean;
 };
 
 export const EmbedSignDocumentClientPage = ({
@@ -48,6 +51,8 @@ export const EmbedSignDocumentClientPage = ({
   fields,
   metadata,
   isCompleted,
+  hidePoweredBy = false,
+  isPlatformOrEnterprise = false,
 }: EmbedSignDocumentClientPageProps) => {
   const { _ } = useLingui();
   const { toast } = useToast();
@@ -131,7 +136,7 @@ export const EmbedSignDocumentClientPage = ({
     }
   };
 
-  useEffect(() => {
+  useLayoutEffect(() => {
     const hash = window.location.hash.slice(1);
 
     try {
@@ -144,6 +149,17 @@ export const EmbedSignDocumentClientPage = ({
       // Since a recipient can be provided a name we can lock it without requiring
       // a to be provided by the parent application, unlike direct templates.
       setIsNameLocked(!!data.lockName);
+
+      if (data.darkModeDisabled) {
+        document.documentElement.classList.add('dark-mode-disabled');
+      }
+
+      if (isPlatformOrEnterprise) {
+        injectCss({
+          css: data.css,
+          cssVars: data.cssVars,
+        });
+      }
     } catch (err) {
       console.error(err);
     }
@@ -325,10 +341,12 @@ export const EmbedSignDocumentClientPage = ({
         <EmbedDocumentFields recipient={recipient} fields={fields} metadata={metadata} />
       </div>
 
-      <div className="bg-primary text-primary-foreground fixed bottom-0 left-0 z-40 rounded-tr px-2 py-1 text-xs font-medium opacity-60 hover:opacity-100">
-        <span>Powered by</span>
-        <Logo className="ml-2 inline-block h-[14px]" />
-      </div>
+      {!hidePoweredBy && (
+        <div className="bg-primary text-primary-foreground fixed bottom-0 left-0 z-40 rounded-tr px-2 py-1 text-xs font-medium opacity-60 hover:opacity-100">
+          <span>Powered by</span>
+          <Logo className="ml-2 inline-block h-[14px]" />
+        </div>
+      )}
     </div>
   );
 };