fix(site): correct navigation state and anchor scrolling (#6)

- make the docs brand link return to the landing site
- keep landing navigation active state synchronized across routes and section links
- tighten sticky-header anchor scroll spacing

packages/landing/test/nav-state.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from "vitest";
+import { getActiveNavItem } from "../src/lib/nav-state";
+
+describe("landing navigation active state", () => {
+  it("tracks known section hashes on the home page", () => {
+    expect(getActiveNavItem("/", "#features")).toBe("features");
+    expect(getActiveNavItem("/", "#quickstart")).toBe("quickstart");
+  });
+
+  it("tracks the Blog route and blog posts", () => {
+    expect(getActiveNavItem("/blog", "")).toBe("blog");
+    expect(getActiveNavItem("/blog/release-notes", "")).toBe("blog");
+  });
+
+  it("does not mark unknown hashes or unrelated routes active", () => {
+    expect(getActiveNavItem("/", "#unknown")).toBeNull();
+    expect(getActiveNavItem("/blog", "#features")).toBe("blog");
+    expect(getActiveNavItem("/other", "#features")).toBeNull();
+  });
+});