fix(run,lanes): prompt autocomplete, per-lane Active runs, compact Changes header

- The run form's prompt box offers suggestions again: `/` lists the run
  cwd's project and user commands and skills plus the CLI built-ins
  (claude lanes only), `@` lists files under the cwd; Enter picks while
  the list is open and sends otherwise. The 2f39f4e rewrite had left a
  bare textarea that ignored both.
- Active runs lists only the current lane's runs and external sessions
  (sessions matched to the lane by longest path-boundary cwd), instead of
  every lane's.
- The Changes panel's git line and its actions are one compact row in one
  card, and the mode/range toolbar is one wrapping row.
- The lane card hides itself when it has nothing to show, instead of
  leaving an empty frame where the git row used to be.

client/src/components/run/__tests__/LaneConsolePane.test.tsx

@@ -331,4 +331,56 @@ describe("LaneConsolePane", () => {
     expect(screen.getByTestId("pane-lane-select")).toBeInTheDocument();
     expect(screen.queryByTestId("console-body")).not.toBeInTheDocument();
   });
+
+  it("lists only this lane's runs and sessions in Active runs, not every lane's", () => {
+    const run = (id: string, laneId: number, promptPreview: string) => ({
+      id,
+      laneId,
+      status: "running",
+      cwd: "/workspace/x",
+      model: null,
+      permissionMode: null,
+      effort: null,
+      resumeSessionId: null,
+      sessionId: null,
+      startedAt: "2026-09-24T01:00:00Z",
+      promptPreview,
+    });
+    const session = (id: string, cwd: string, name: string) =>
+      ({
+        id,
+        cwd,
+        name,
+        model: null,
+        source: "local",
+        started_at: "2026-09-24T01:00:00Z",
+      }) as never;
+    render(
+      <MemoryRouter>
+        <LaneConsolePane
+          {...baseProps()}
+          lanes={[
+            LANE,
+            { ...LANE, id: 2, cwd: "/workspace/b" },
+            // Nested inside lane 1: its sessions are ITS own, by longest prefix.
+            { ...LANE, id: 3, cwd: "/workspace/a/nested" },
+          ]}
+          activeRuns={{ items: [run("r1", 1, "mine"), run("r2", 2, "other lane's")] as never }}
+          externalSessions={[
+            session("s1", "/workspace/a/src", "my session"),
+            session("s2", "/workspace/b", "b session"),
+            session("s3", "/workspace/a/nested/x", "nested session"),
+            session("s4", "/workspace/ab", "sibling prefix"),
+          ]}
+        />
+      </MemoryRouter>
+    );
+    fireEvent.click(screen.getByRole("button", { name: /2 active runs/ }));
+    expect(screen.getByText("mine")).toBeTruthy();
+    expect(screen.getByText("my session")).toBeTruthy();
+    expect(screen.queryByText("other lane's")).toBeNull();
+    expect(screen.queryByText("b session")).toBeNull();
+    expect(screen.queryByText("nested session")).toBeNull();
+    expect(screen.queryByText("sibling prefix")).toBeNull();
+  });
 });