feat: auto-update on start for global installs

On relay start, if a newer version is available and running from a global
install, automatically runs bun/npm install -g in the background. bunx users
get a hint to use @latest instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: adriandmitroca

src/cli.ts

@@ -49,14 +49,24 @@ function isRunningViaBunx(): boolean {
   return import.meta.dir.includes("/.bun/install/cache/");
 }
 
-/** Silently check for updates and print a one-liner if a newer version is available. */
+/** Silently check for updates and auto-apply if on a global install, or print hint for bunx. */
 async function checkForUpdates() {
   const latest = await fetchLatestVersion();
-  if (latest && latest !== VERSION) {
-    const hint = isRunningViaBunx()
-      ? `bunx ${NPM_PACKAGE}@latest start`
-      : `relay update`;
-    console.log(`${DIM}relay v${latest} is available (you have v${VERSION}). Run: ${hint}${RESET}`);
+  if (!latest || latest === VERSION) return;
+
+  if (isRunningViaBunx()) {
+    console.log(`${DIM}relay v${latest} is available. Run: bunx ${NPM_PACKAGE}@latest start${RESET}`);
+    return;
+  }
+
+  console.log(`${DIM}relay v${latest} available — auto-updating...${RESET}`);
+  const bunCheck = await Bun.$`which bun`.quiet().nothrow();
+  const installCmd = bunCheck.exitCode === 0
+    ? `bun install -g ${NPM_PACKAGE}@latest`
+    : `npm install -g ${NPM_PACKAGE}@latest`;
+  const result = await Bun.$`sh -c ${installCmd}`.quiet().nothrow();
+  if (result.exitCode === 0) {
+    console.log(`${DIM}Updated to v${latest}. Restart relay to apply.${RESET}`);
   }
 }