docs: Add intros for the build and storage command pages

cloud_docs/reference/cli/commands/build/_build.md

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+# scloud build
+
+The `scloud build` commands cover the Cloud build stage of a deploy: reading a deployment's build log and managing the secrets the build can use. Build-time errors surface in the build log, not in the runtime logs that `scloud log` fetches.
+
+Build secrets cover credentials the build needs and your source code shouldn't carry. See [Private dependencies](/cloud/reference/private-dependencies) for the setup that uses them, and [Passwords, secrets, and environment variables](/cloud/concepts/passwords-secrets-env-vars) for the values your server reads at runtime.
+
+For where the build sits in the deploy lifecycle, see [Deployments](/cloud/concepts/deployments). To work through a failed build step by step, see [Recover from a failed deploy](/cloud/guides/recover-from-a-failed-deploy).

cloud_docs/reference/cli/commands/storage/_storage.md

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+# scloud storage
+
+The `scloud storage` commands manage your project's storages and the files in them. Your app uploads those files while it runs. From the terminal you can list what users uploaded, download a file to debug it, or upload one yourself.
+
+Decide who may read a storage before you create it, because that choice cannot be changed later.
+
+For how your server connects to these storages, see [File uploads](/concepts/endpoints-and-apis/file-uploads#configure-a-storage-provider) in the framework documentation.