fix: fix prepare-preview-builds.ts (#444)

Deps might actually be undefined if some of our packages don't depend on
any others (like for the `account-api`).

So we need to add fallback records for those cases.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Ensures the preview build script tolerates packages without dependency
sections.
> 
> - In `scripts/prepare-preview-builds.ts`, default `dependencies` and
`peerDependencies` to `{}` before mutation when moving peer deps to
`dependencies` and when pinning workspace versions in
`dependencies`/`devDependencies`
> - Prevents errors when a package lacks
`dependencies`/`peerDependencies`
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
d09be21. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: ccharly

scripts/prepare-preview-builds.ts

@@ -150,8 +150,8 @@ async function updateWorkspacePackagesWithPreviewInfo(
     const peerDepKey = 'peerDependencies';
     if (peerDepKey in pkgJson.content) {
       const depKey = 'dependencies';
-      const deps = pkgJson.content[depKey] as DependenciesRecord;
-      const peerDeps = pkgJson.content[peerDepKey] as DependenciesRecord;
+      const deps: DependenciesRecord = pkgJson.content[depKey] ?? {};
+      const peerDeps: DependenciesRecord = pkgJson.content[peerDepKey] ?? {};
 
       for (const { name, version } of previewPkgs) {
         // Only consider dependenc that refers to a local workspace package
@@ -173,7 +173,7 @@ async function updateWorkspacePackagesWithPreviewInfo(
     // of that package instead, and `yarn` will resolve this using the global resolutions
     // (see `updateWorkspaceResolutions`)
     for (const depKey of ['dependencies', 'devDependencies']) {
-      const deps = pkgJson.content[depKey] as DependenciesRecord;
+      const deps: DependenciesRecord = pkgJson.content[depKey] ?? {};
 
       for (const { name, version } of previewPkgs) {
         // Only consider dependenc that refers to a local workspace package