feat(HAI-059): add horizontal scroll support for board columns

- Update board grid to use minmax(260px, 1fr) for minimum column widths
- Replace overflow: hidden with overflow-x: auto for horizontal scrolling
- Add min-width: 260px to column class for consistent sizing
- Add Board test verifying id='board' attribute for scroll targeting

packages/dashboard/app/components/__tests__/Board.test.tsx

@@ -39,6 +39,12 @@ describe("Board", () => {
     expect(main.className).toContain("board");
   });
 
+  it("renders with id='board' for scroll targeting", () => {
+    renderBoard();
+    const main = screen.getByRole("main");
+    expect(main.id).toBe("board");
+  });
+
   it("renders all 5 columns", () => {
     renderBoard();
     for (const col of COLUMNS) {

packages/dashboard/app/styles.css

@@ -99,11 +99,12 @@ html, body {
 /* === Board === */
 .board {
   display: grid;
-  grid-template-columns: repeat(5, 1fr);
+  grid-template-columns: repeat(5, minmax(260px, 1fr));
   gap: 12px;
   padding: 16px 24px;
   height: calc(100vh - 57px);
-  overflow: hidden;
+  overflow-x: auto;
+  overflow-y: hidden;
 }
 
 .column {
@@ -113,6 +114,7 @@ html, body {
   border-radius: var(--radius-lg);
   border: 1px solid var(--border);
   overflow: hidden;
+  min-width: 260px;
   min-height: 0;
   transition: border-color 0.2s;
 }

packages/dashboard/public/style.css

@@ -76,11 +76,12 @@ html, body {
 /* === Board === */
 .board {
   display: grid;
-  grid-template-columns: repeat(5, 1fr);
+  grid-template-columns: repeat(5, minmax(260px, 1fr));
   gap: 12px;
   padding: 16px 24px;
   height: calc(100vh - 57px);
-  overflow: hidden;
+  overflow-x: auto;
+  overflow-y: hidden;
 }
 
 .column {
@@ -90,6 +91,7 @@ html, body {
   border-radius: var(--radius-lg);
   border: 1px solid var(--border);
   overflow: hidden;
+  min-width: 260px;
   min-height: 0;
   transition: border-color 0.2s;
 }