fix(workspace): stop the console remounting, and the idle polling re-renders

The Workspace page rendered `ConsoleArea` from two sites, picked by
`currentLane`. Every flip of that value unmounted the whole console
subtree and mounted it again at the other site: the terminal died, the
run history went with it, and `LaneConsolePane`'s lane-switch effect
wiped a half-typed prompt. It flipped on every page load (lanes arrive,
`refreshLanes` selects `lanes[0]`), on a lane being removed, and on any
refetch that re-picked the selection.

`lane-detail` is now always rendered and holds the only `ConsoleArea`;
the header and info block are the conditional parts. Same rule the
RunConsole already followed one level down — collapse with CSS, never by
unmounting — now enforced above it too.

Second half: every poller fed `setState` a brand-new object graph each
tick, re-rendering the lane strip, the card and the console area several
times a minute on a completely idle dashboard. `keepIfSame` keeps the
previous reference when the payload is value-identical, applied to the
5 s run/session poll, the lane list and counts, the `lane_update` WS
branch, and LaneCard's git/runtime/locks pollers.

Verified: npm run test:client (44 files / 454 tests), tsc --noEmit
clean, check-headers.sh clean. The Run screen snapshot was regenerated —
the diff is the added `<section>` wrapper and one indent level, no
content change.

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

@@ -584,6 +584,19 @@ describe("Workspace — the console is its own section", () => {
     const body = screen.getByTestId("console-body");
     expect(detail.contains(body)).toBe(true);
   });
+
+  // A SECOND render site for the console is what let `currentLane` flipping
+  // (lanes arriving on mount, the selected lane removed, a refetch re-picking
+  // the selection) unmount the terminal and wipe a half-typed prompt. It must
+  // sit inside `lane-detail` in BOTH states, so React never has to move it.
+  it("keeps the console at one render site whether or not a lane is selected", async () => {
+    lanesToReturn = [];
+    countsToReturn = { total: 0, running: 0, needs_you: 0, dead: 0 };
+    await renderWorkspace();
+
+    const detail = screen.getByTestId("lane-detail");
+    expect(detail.contains(screen.getByTestId("console-body"))).toBe(true);
+  });
 });
 
 describe("Workspace — proof gallery", () => {