fix(auto-update): align PACKAGE_NAME with published package name (#3129)

Changed PACKAGE_NAME from 'oh-my-openagent' to 'oh-my-opencode' in
auto-update-checker/constants.ts to match package.json. This fixes
getCachedVersion() returning null, causing 'unknown' in version toast.

TDD: red-green confirmed. 39 tests pass, tsc clean.

Closes #3129

src/hooks/auto-update-checker/constants.test.ts

@@ -1,5 +1,7 @@
 import { describe, expect, it } from "bun:test"
+import { readFileSync } from "node:fs"
 import { join } from "node:path"
+import { fileURLToPath } from "node:url"
 import { getOpenCodeCacheDir } from "../../shared/data-path"
 
 describe("auto-update-checker constants", () => {
@@ -11,4 +13,17 @@ describe("auto-update-checker constants", () => {
       join(getOpenCodeCacheDir(), "packages", "node_modules", PACKAGE_NAME, "package.json")
     )
   })
+
+  it("PACKAGE_NAME matches the published package.json name", async () => {
+    // given the canonical package.json shipped with the plugin
+    const here = fileURLToPath(import.meta.url)
+    const repoPackageJsonPath = join(here, "..", "..", "..", "..", "package.json")
+    const repoPackageJson = JSON.parse(readFileSync(repoPackageJsonPath, "utf-8")) as { name: string }
+
+    // when the auto-update-checker constants are loaded
+    const { PACKAGE_NAME } = await import(`./constants?test=${Date.now()}`)
+
+    // then PACKAGE_NAME equals the actually published package name
+    expect(PACKAGE_NAME).toBe(repoPackageJson.name)
+  })
 })