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");
+  });
+});

packages/dashboard/app/styles.css

@@ -1300,6 +1300,23 @@ html, body {
    On narrow viewports (≤768px) the modal goes full-screen, action buttons wrap,
    and spacing is reduced to stay usable on screens as small as 320px. */
 @media (max-width: 768px) {
+  /* Board: horizontal scroll-snap for swipe-between-columns */
+  .board {
+    display: flex;
+    overflow-x: auto;
+    overflow-y: hidden;
+    -webkit-overflow-scrolling: touch;
+    scroll-snap-type: x mandatory;
+    padding: 12px;
+    gap: 12px;
+  }
+
+  .board > .column {
+    min-width: 280px;
+    flex-shrink: 0;
+    scroll-snap-align: start;
+  }
+
   .modal-overlay {
     padding-top: 0;
     align-items: stretch;