feat(cli): add self-update service

Check the npm registry (at most once per 24h, file-locked) for newer
@opencode-ai/cli releases and act on a host-level autoupdate policy read
from config. Apply patch updates automatically, confirm minor updates
interactively, and never auto-update across majors. Skip local installs
and honor the disable flag. Wired into the default TUI command
(interactive) and serve (background).

packages/cli/src/services/updater.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, test } from "bun:test"
+import { action, decodePolicy } from "./updater"
+
+describe("updater", () => {
+  test("reads autoupdate from JSONC", () => {
+    expect(decodePolicy('{ // preference\n "autoupdate": "notify",\n}')).toBe("notify")
+    expect(decodePolicy('{ "autoupdate": false }')).toBe(false)
+    expect(decodePolicy('{ "autoupdate": "invalid" }')).toBeUndefined()
+  })
+
+  test("automatically updates patches", () => {
+    expect(action("1.2.3", "1.2.4", true, false)).toBe("upgrade")
+    expect(action("1.2.3", "1.2.4", "notify", true)).toBe("confirm")
+    expect(action("1.2.3", "1.2.4", false, true)).toBe("none")
+  })
+
+  test("requires an interactive confirmation for minors", () => {
+    expect(action("1.2.3", "1.3.0", true, true)).toBe("confirm")
+    expect(action("1.2.3", "1.3.0", true, false)).toBe("none")
+  })
+
+  test("never automatically updates majors", () => {
+    expect(action("1.2.3", "2.0.0", true, true)).toBe("none")
+  })
+})