feat(lanes,ui): per-lane git surface — Changes panel, VS Code-style diff, branch-aware Add lane, redesigned tooltips (#34, #35)

- Changes card beside lane detail with five modes: Files tree, overview,
  Review (whole diff, per-file collapse), single file, commit history.
- LaneDiffView: unified / side-by-side with independent scroll on both axes
  and mirrored scrollLeft, expand/collapse context, intra-line emphasis.
- Staged-only commit box; git actions (fetch/pull/push/stage/unstage/
  discard/commit/switch/branch-create/branch-delete) guarded in git-ops.js.
- Server: git-diff.js + git-ops.js behind GET /api/lanes/:id/git/* and
  POST /api/lanes/:id/git/:action; gitFacts gains upstream/ahead/behind.
- Add lane: new/existing branch, current branch, worktree list, prefill
  from the git bar's "New lane here"; /api/run/cwds gains a repo kind.
- GlobalTooltip upgrades every native title into a themed anchored bubble;
  chart/info popovers use theme tokens.

client/src/pages/__tests__/Workspace.changesPanel.test.tsx

@@ -0,0 +1,182 @@
+/**
+ * @file Workspace.changesPanel.test.tsx
+ * @description The Changes panel is ONE control: it steps narrow → 50/50 →
+ * 70/30 → closed, and the rail reopens it narrow. The width survives a reload.
+ * All of it lives in localStorage and reaches no server — the same rule as the
+ * lane strip's order.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { render, act, cleanup, screen, fireEvent } from "@testing-library/react";
+import { MemoryRouter } from "react-router-dom";
+import i18n from "i18next";
+
+// Hoisted: `vi.mock`'s factory is lifted above the module body, so the
+// fixtures it reads have to be lifted with it.
+const { HOME, LANE_A, LANE_B } = vi.hoisted(() => {
+  const laneStub = (id: number, cwd: string) => ({
+    id,
+    title: `lane-${id}`,
+    cwd,
+    branch: null,
+    kind: "adopted",
+    source_repo: null,
+    pipeline: "default",
+    session_id: null,
+    run_id: null,
+    stage: "idle",
+    stage_since: null,
+    status: "idle",
+    gate_decision: null,
+    ci_status: null,
+    needs_action: null,
+    links: {},
+    stages: {},
+    notes: null,
+    pipeline_name: "Default",
+    pipeline_nodes: [],
+    progress: 0,
+    stage_seconds: null,
+    last_event_seconds: null,
+    liveness: "idle",
+    detected_stage: null,
+    detected_signal: null,
+    slot: null,
+    ports: {},
+    active_feature_id: null,
+  });
+  return {
+    HOME: { kind: "home", path: "/Users/tester", label: "Home" },
+    LANE_A: laneStub(1, "/workspace/alpha"),
+    LANE_B: laneStub(2, "/workspace/beta"),
+  };
+});
+
+vi.mock("../../lib/api", async (importOriginal) => {
+  const actual = await importOriginal<Record<string, unknown>>();
+  const r = (value: unknown) => vi.fn().mockResolvedValue(value);
+  return {
+    ...actual,
+    api: {
+      run: {
+        list: r({ items: [] }),
+        history: r({ items: [] }),
+        binary: r({ found: true, path: "/usr/bin/claude" }),
+        cwds: r({ items: [HOME] }),
+        files: r({ items: [] }),
+        start: r({ id: "run-1", status: "running" }),
+        get: r({ id: "run-1", status: "running" }),
+      },
+      lanes: {
+        list: r({
+          lanes: [LANE_A, LANE_B],
+          counts: { total: 2, running: 0, needs_you: 0, dead: 0 },
+        }),
+        pipelines: r({ pipelines: [] }),
+        git: r({ available: false }),
+        runtime: r({ up: false, ports: {}, lastError: null }),
+        features: { list: r({ features: [] }), show: r({ feature: null }) },
+        proof: { list: r({ features: [] }), imageUrl: () => "" },
+      },
+      aiRouters: { list: r({ items: [] }) },
+      sessions: { list: r({ sessions: [], total: 0, limit: 50, offset: 0 }) },
+    },
+  };
+});
+
+vi.mock("../../lib/eventBus", () => ({
+  eventBus: {
+    subscribe: () => () => {},
+    publish: () => {},
+    onConnection: () => () => {},
+    connected: true,
+    setConnected: () => {},
+  },
+}));
+
+import { Workspace } from "../Workspace";
+
+class ObserverStub {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+  takeRecords() {
+    return [];
+  }
+}
+globalThis.ResizeObserver =
+  globalThis.ResizeObserver || (ObserverStub as unknown as typeof ResizeObserver);
+
+async function settle() {
+  await act(async () => {
+    await new Promise((r) => setTimeout(r, 0));
+    await new Promise((r) => setTimeout(r, 0));
+  });
+}
+
+beforeEach(() => {
+  i18n.changeLanguage("en");
+});
+
+afterEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("Workspace — the Changes panel's width", () => {
+  beforeEach(() => window.localStorage.clear());
+
+  async function openPanel() {
+    render(
+      <MemoryRouter initialEntries={["/run"]}>
+        <Workspace />
+      </MemoryRouter>
+    );
+    await settle();
+    // Open/closed is itself remembered, so the second mount of a test comes up
+    // already open — clicking the rail then would close it.
+    const rail = screen.queryByTestId("lane-changes-expand");
+    if (rail) {
+      fireEvent.click(rail);
+      await settle();
+    }
+  }
+
+  it("steps narrow → 50/50 → 70/30 → closed on one control", async () => {
+    await openPanel();
+    const card = () => screen.getByTestId("lane-changes-card");
+    expect(card().className).toContain("w-[28rem]");
+
+    fireEvent.click(screen.getByTestId("lane-changes-resize"));
+    expect(card().className).toContain("w-1/2");
+
+    fireEvent.click(screen.getByTestId("lane-changes-resize"));
+    expect(card().className).toContain("w-[70%]");
+
+    // Past the widest step the panel closes — and reopens narrow, not back at
+    // 70/30, which is why closing resets the width.
+    fireEvent.click(screen.getByTestId("lane-changes-resize"));
+    await settle();
+    expect(screen.queryByTestId("lane-changes-card")).toBeNull();
+
+    fireEvent.click(screen.getByTestId("lane-changes-expand"));
+    await settle();
+    expect(card().className).toContain("w-[28rem]");
+  });
+
+  it("remembers the width across a reload, and never asks the server", async () => {
+    await openPanel();
+    fireEvent.click(screen.getByTestId("lane-changes-resize"));
+    expect(window.localStorage.getItem("agenthub.workspace.changesSize")).toBe("half");
+
+    cleanup();
+    await openPanel();
+    expect(screen.getByTestId("lane-changes-card").className).toContain("w-1/2");
+  });
+
+  it("keeps the rail as the only way back in", async () => {
+    await openPanel();
+    expect(screen.queryByTestId("lane-changes-collapse")).toBeNull();
+    expect(screen.getByTestId("lane-changes-card")).toBeInTheDocument();
+  });
+});