feat(web): red border on a server card whose connection attempt failed (#1621)

Flags the server whose last connection attempt failed with a red card
border, cleared when another server is connected or a new connection is
attempted — a persistent, at-a-glance companion to the failure toast and
the auto-opened monitoring column.

- App tracks `failedServerId`: set in onToggleConnection's non-auth
  handshake catch, cleared at the start of any new connect attempt. It is
  deliberately kept out of resetSessionScopedUiState, since the failure's
  own `disconnect` event would otherwise clear it the same tick (that same
  event clears `activeServer`, which is why the flag is tracked separately).
- New `errored` Card theme variant (red border via a new
  `--inspector-error-border` token), mirroring the `highlighted` green
  border. Precedence: disabled (dimmed) > errored > highlighted.
- Plumbed `erroredServerId` through InspectorView → ServerListScreen →
  ServerCard (`errored` prop).

Full `npm run ci` passes (validate + coverage + smoke + storybook).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw

clients/web/src/components/groups/ServerCard/ServerCard.test.tsx

@@ -363,4 +363,56 @@ describe("ServerCard", () => {
       expect(onClearHighlight).toHaveBeenCalledTimes(1);
     });
   });
+
+  describe("connection-failed border (#1621)", () => {
+    it("draws the red errored-variant border when errored", () => {
+      const { container } = renderWithMantine(
+        <ServerCard {...baseProps} connection={disconnected} errored />,
+      );
+      expect(
+        container.querySelector('[data-variant="errored"]'),
+      ).not.toBeNull();
+    });
+
+    it("does not draw the errored border when not errored", () => {
+      const { container } = renderWithMantine(
+        <ServerCard {...baseProps} connection={disconnected} />,
+      );
+      expect(container.querySelector('[data-variant="errored"]')).toBeNull();
+    });
+
+    it("prefers the dimmed (disabled) variant over the errored border", () => {
+      // A dimmed card (another server active) is inert; that wins over the
+      // error border so the card can't look interactive.
+      const { container } = renderWithMantine(
+        <ServerCard
+          {...baseProps}
+          connection={disconnected}
+          activeServer="other"
+          errored
+        />,
+      );
+      expect(
+        container.querySelector('[data-variant="disabled"]'),
+      ).not.toBeNull();
+      expect(container.querySelector('[data-variant="errored"]')).toBeNull();
+    });
+
+    it("prefers the errored border over the freshly-added highlight", () => {
+      const { container } = renderWithMantine(
+        <ServerCard
+          {...baseProps}
+          connection={disconnected}
+          errored
+          highlighted
+        />,
+      );
+      expect(
+        container.querySelector('[data-variant="errored"]'),
+      ).not.toBeNull();
+      expect(
+        container.querySelector('[data-variant="highlighted"]'),
+      ).toBeNull();
+    });
+  });
 });