deploy deprecation notice (#1972)

* deploy deprecation notice

* avoid period confusion

Author: mbostock

src/bin/observable.ts

@@ -81,7 +81,7 @@ try {
   build        generate a static site
   login        sign-in to Observable
   logout       sign-out of Observable
-  deploy       deploy an app to Observable
+  deploy       deploy an app to Observable [deprecated]
   whoami       check authentication status
   convert      convert an Observable notebook to Markdown
   help         print usage information

src/deploy.ts

@@ -84,13 +84,18 @@ type DeployTargetInfo =
   | {create: true; workspace: {id: string; login: string}; projectSlug: string; title: string; accessLevel: string}
   | {create: false; workspace: {id: string; login: string}; project: GetProjectResponse};
 
-/** Deploy a project to ObservableHQ */
 export async function deploy(deployOptions: DeployOptions, effects = defaultEffects): Promise<void> {
   Telemetry.record({event: "deploy", step: "start", force: deployOptions.force});
   effects.clack.intro(`${inverse(" observable deploy ")} ${faint(`v${process.env.npm_package_version}`)}`);
-
+  effects.clack.log.warn(
+    wrapAnsi(
+      `Deploying data apps to Observable Cloud is now deprecated. Please migrate your data app to another static site hosting provider, such as GitHub Pages, Render, Cloudflare Pages, Vercel, or Netlify. For more details, please see: ${underline(
+        "https://observablehq.com/release-notes/2025-04-15-deprecating-observable-cloud"
+      )}`,
+      effects.outputColumns
+    )
+  );
   const deployInfo = await new Deployer(deployOptions, effects).deploy();
-
   effects.clack.outro(`Deployed app now visible at ${link(deployInfo.url)}`);
   Telemetry.record({event: "deploy", step: "finish"});
 }