feat(ui): pinned modifier inspection panel

- Create ModifierPinnedPanel.tsx: fixed-position side panel with piece
  header, modifier list (label + describe() value), and close button
- Board.tsx: add onPieceClick prop, fire on piece click (distinct from drag)
- GameView.tsx: add pinnedPieceId state; clicking a piece toggles pin;
  clicking same piece again or × closes panel; panel renders fixed right-4
- 2 new e2e tests: click b1 pins panel with 'knight' text; × dismisses it

packages/chess/e2e/modifier-profiles.spec.ts

@@ -191,6 +191,58 @@ test.describe('Modifier Profiles — hover tooltip (T24)', () => {
   });
 });
 
+// ── T25: Pinned modifier inspection panel ────────────────────────────────
+
+test.describe('Modifier Profiles — pinned panel (T25)', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+
+    // Clear any stale autosave so Play Solo starts a fresh game.
+    await page.evaluate(() => {
+      for (let i = localStorage.length - 1; i >= 0; i--) {
+        const key = localStorage.key(i);
+        if (key !== null && key.startsWith('paratype-chess:v2:autosave:')) {
+          localStorage.removeItem(key);
+        }
+      }
+      localStorage.removeItem('paratype-chess:v1:autosave');
+    });
+
+    // Navigate into the game WITHOUT opening the rules drawer —
+    // the board must remain fully interactive.
+    await page.locator('[data-action="play-solo"]').click();
+    await page.waitForURL('**/game');
+  });
+
+  test('click piece pins side panel', async ({ page }) => {
+    // Click the b1 square — white knight in the classic starting position.
+    await page.click('[data-square="b1"]');
+
+    // The pinned panel must appear and identify the piece.
+    await expect(
+      page.locator('[data-testid="modifier-pinned-panel"]'),
+    ).toBeVisible({ timeout: 2000 });
+    await expect(
+      page.locator('[data-testid="modifier-pinned-panel"]'),
+    ).toContainText(/knight/i);
+  });
+
+  test('closing pinned panel removes it', async ({ page }) => {
+    // Pin the panel.
+    await page.click('[data-square="b1"]');
+    await expect(
+      page.locator('[data-testid="modifier-pinned-panel"]'),
+    ).toBeVisible({ timeout: 2000 });
+
+    // Dismiss via the close button.
+    await page.click('[data-testid="close-pinned-panel"]');
+
+    await expect(
+      page.locator('[data-testid="modifier-pinned-panel"]'),
+    ).not.toBeVisible({ timeout: 1000 });
+  });
+});
+
 // ── T26: Lobby profile picker + GameView badge ─────────────────────────
 
 test.describe('Modifier Profiles — Lobby integration (T26)', () => {