merge: SP5 live-tail — pub/sub + 3 stream endpoints + frontend tail integration

Brings the SP5 live-tail implementation into main:

Backend
  * EventBus (cyclone.pubsub): per-kind fan-out with drop-oldest overflow
  * FastAPI lifespan initializes the bus + db once per process
  * store.add() publishes claim_written / remittance_written /
    activity_recorded events on every batch write
  * GET /api/{claims,remittances,activity}/stream: NDJSON snapshot +
    live subscription + 15s idle heartbeat
  * EventBus.unsubscribe() lets the tail loop release its queue on
    client disconnect (no queue leak per open stream)

Frontend
  * src/lib/tail-stream.ts: streamTail() async-generator over fetch
  * src/store/tail-store.ts: zustand with FIFO cap 10k per slice
  * src/hooks/useTailStream.ts: connecting/live/reconnecting/stalled/error/closed
    state machine with 1→2→4→8→16→30s backoff
  * src/hooks/useMergedTail.ts: base + tail merge with filter
  * src/components/TailStatusPill.tsx: badge + Reconnect button
  * Claims, Remittances, ActivityLog pages wired to the tail

Tests
  * 437 backend tests pass (was 418 before SP5)
  * 154 frontend tests pass (was 124)
  * npm run typecheck clean
  * end-to-end smoke: open /api/claims/stream, POST 837, see new claims
    arrive in real time without refresh

# Conflicts:
#	src/pages/ActivityLog.tsx
#	src/pages/Remittances.test.tsx
#	src/pages/Remittances.tsx

src/pages/Remittances.test.tsx

@@ -10,6 +10,7 @@ import { describe, expect, it, vi, beforeEach } from "vitest";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { Remittances } from "./Remittances";
 import { api } from "@/lib/api";
+import { useTailStore } from "@/store/tail-store";
 
 // Module-level mock: vitest hoists `vi.mock` calls above imports. We only
 // stub the method this page touches via the `useRemittances` hook.
@@ -23,6 +24,18 @@ vi.mock("@/lib/api", () => ({
   },
 }));
 
+// Mock the live-tail hook so the page renders the pill in the settled
+// `live` state without driving the real streamTail parser. The hook's
+// own test file (`useTailStream.test.ts`) covers the lifecycle in depth.
+vi.mock("@/hooks/useTailStream", () => ({
+  useTailStream: vi.fn(() => ({
+    status: "live",
+    lastEventAt: null,
+    error: null,
+    forceReconnect: vi.fn(),
+  })),
+}));
+
 /**
  * Minimal `render` helper using react-dom/client + act(). Mirrors the
  * `renderIntoContainer` helper in `Reconciliation.test.tsx` — see that
@@ -178,6 +191,10 @@ const SAMPLE_REMITS = [
 describe("Remittances", () => {
   beforeEach(() => {
     vi.clearAllMocks();
+    // Singleton tail-store: clear the remittances slice between tests
+    // so a tail-arrival case (if added later) doesn't see rows from a
+    // previous test.
+    useTailStore.getState().reset("remittances");
     (
       api.listRemittances as unknown as ReturnType<typeof vi.fn>
     ).mockResolvedValue({
@@ -389,4 +406,36 @@ describe("Remittances", () => {
 
     unmount();
   });
+
+  // -------------------------------------------------------------------
+  // Live-tail status pill (sub-project 5, Phase 5 Task 23, optional
+  // page-level test). Cheap smoke check: the toolbar renders the pill
+  // with the `live` label whenever the mocked stream is settled. The
+  // hook's lifecycle is covered exhaustively in its own test file.
+  // -------------------------------------------------------------------
+
+  it("test_status_pill_shows_live_in_toolbar", async () => {
+    (
+      api.listRemittances as unknown as ReturnType<typeof vi.fn>
+    ).mockResolvedValue({
+      items: [],
+      total: 0,
+      returned: 0,
+      has_more: false,
+    });
+
+    const { unmount } = renderIntoContainer(React.createElement(Remittances));
+
+    // Wait for the empty-state to mount — once the page body is rendered,
+    // the toolbar (and thus the pill) is in the DOM.
+    await waitForText("Remittances · awaiting first 835");
+
+    const pill = document.body.querySelector(
+      '[data-testid="tail-status-pill"]',
+    );
+    expect(pill).not.toBeNull();
+    expect(pill?.textContent).toContain("Live");
+
+    unmount();
+  });
 });