test: cover post-merge gaps in utils, services, and hooks

Adds specs for the files added or modified in the recent merge that
weren't yet covered: oauthReturnPath, withATProtoImages, link,
displayLanguage, and the useGitHubContent / useImageUpload /
useNoteFreshness hooks. Locks in the new pullLatest contract
({raw, failureStatus}) and the fetchLatestSha branch semantics
(ok/unauthorized/offline).

src/modules/user/service/oauthReturnPath.spec.ts

@@ -0,0 +1,30 @@
+import { beforeEach, describe, expect, it } from "vitest"
+
+import {
+  consumeGithubOAuthReturnPath,
+  GITHUB_OAUTH_RETURN_PATH_KEY
+} from "./oauthReturnPath"
+
+describe("consumeGithubOAuthReturnPath", () => {
+  beforeEach(() => {
+    sessionStorage.clear()
+  })
+
+  it("returns the stored path and clears the key", () => {
+    sessionStorage.setItem(GITHUB_OAUTH_RETURN_PATH_KEY, "/alice/notes")
+
+    expect(consumeGithubOAuthReturnPath()).toBe("/alice/notes")
+    expect(sessionStorage.getItem(GITHUB_OAUTH_RETURN_PATH_KEY)).toBeNull()
+  })
+
+  it("returns null when nothing is stored", () => {
+    expect(consumeGithubOAuthReturnPath()).toBeNull()
+  })
+
+  it("returns null on the second call (consume-once semantics)", () => {
+    sessionStorage.setItem(GITHUB_OAUTH_RETURN_PATH_KEY, "/x")
+
+    expect(consumeGithubOAuthReturnPath()).toBe("/x")
+    expect(consumeGithubOAuthReturnPath()).toBeNull()
+  })
+})