feat(KB-167): add mobile scroll-snap CSS to board columns

- Add scroll-snap-type: x mandatory to .board in ≤768px media query
- Set scroll-snap-align: start and flex-shrink: 0 on .column for swipe navigation
- Enable -webkit-overflow-scrolling: touch for smooth iOS scrolling
- Add mobile-scroll-snap test suite asserting snap rules inside @media block

packages/dashboard/app/__tests__/mobile-scroll-snap.test.ts

@@ -0,0 +1,39 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "fs";
+import { resolve } from "path";
+
+const css = readFileSync(
+  resolve(__dirname, "../styles.css"),
+  "utf-8",
+);
+
+describe("mobile scroll-snap CSS", () => {
+  it("contains scroll-snap-type: x mandatory", () => {
+    expect(css).toContain("scroll-snap-type: x mandatory");
+  });
+
+  it("contains scroll-snap-align: start", () => {
+    expect(css).toContain("scroll-snap-align: start");
+  });
+
+  it("contains -webkit-overflow-scrolling: touch", () => {
+    expect(css).toContain("-webkit-overflow-scrolling: touch");
+  });
+
+  it("contains flex-shrink: 0", () => {
+    expect(css).toContain("flex-shrink: 0");
+  });
+
+  it("scroll-snap rules are inside a @media block", () => {
+    // Extract all @media blocks and verify snap rules exist within one
+    const mediaBlockRegex = /@media\s*\([^)]*max-width:\s*768px[^)]*\)\s*\{/g;
+    const mediaStart = css.search(mediaBlockRegex);
+    expect(mediaStart).toBeGreaterThanOrEqual(0);
+
+    // Get the content after the media query opening
+    const afterMedia = css.slice(mediaStart);
+    // Find the scroll-snap-type within this media block
+    expect(afterMedia).toContain("scroll-snap-type: x mandatory");
+    expect(afterMedia).toContain("scroll-snap-align: start");
+  });
+});