feat(frontend): phase progress dots (B) + compact sidebar redesign (C)

B — WorkflowBar renders F1..F8 as colored ring-dots (no phase-name text):
green=done, amber=running (subtle pulse), red=error, gray=pending; green
connectors lead the active dot, each dot carries data-state. Lightweight
error signal: sessionStore gains `phaseError`, set when an info event has
level=error during the active phase, cleared on the next ui_request.

C — denser single-line session rows (inline status dot + name, py-1), a
3-level type hierarchy (L1 SESSIONS / L2 section+group headers / L3 names),
and the "No group" label removed (ungrouped render after the last group,
guarded so the empty-state still teaches when there are zero groups).

Live-verified with Playwright (all four dot states, sidebar hierarchy, and
E's deferred activity-panel check). Frontend 93/93, tsc -b clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/WorkflowBar.test.tsx

@@ -20,3 +20,19 @@ test("no phase highlighted when currentPhase is null", () => {
     expect(screen.getByTestId(`phase-${id}`)).toHaveAttribute("data-active", "false");
   }
 });
+
+test("dots carry done / running / pending states around the active phase", () => {
+  useSessionStore.getState().setPhase("F3");
+  render(<WorkflowBar />);
+  expect(screen.getByTestId("phase-F1")).toHaveAttribute("data-state", "done");
+  expect(screen.getByTestId("phase-F3")).toHaveAttribute("data-state", "running");
+  expect(screen.getByTestId("phase-F5")).toHaveAttribute("data-state", "pending");
+});
+
+test("the active dot turns to the error state when phaseError flags it", () => {
+  const st = useSessionStore.getState();
+  st.applyEvent({ type: "ui_request", ui_request: { id: "u", widget: "select", phase: "F3_x" } });
+  st.applyEvent({ type: "info", level: "error", text: "boom" });
+  render(<WorkflowBar />);
+  expect(screen.getByTestId("phase-F3")).toHaveAttribute("data-state", "error");
+});