docs(lanes): document the Workspace split terminal view

docs/LANES.md

@@ -310,6 +310,7 @@ The dashboard web UI merges lanes and runs into a single **Workspace** page acce
 - **Header** — the page title and four counters (`lanes`, `running`, `needs you`, `dead`), plus Add lane. The `needs you` and `dead` counters appear only when they are non-zero, so a quiet header means nothing is waiting on a human.
 - **Detail panel** — the selected lane's declared stage, its inferred stage when detection leads, a full-width pipeline map, and a legend naming all five node states plus the dashed-amber inferred treatment.
 - **Terminal** — a real interactive terminal (xterm.js) displaying the tmux session's PTY output, with full support for interactive commands, editors, and pagers. A live run keeps its rendered history and scroll position when scrolling.
+- **Split view** — a layout toggle (1 / 2 / 4 panes) renders that many independent terminal panes side by side (`grid-cols-2` for 2, a 2×2 grid for 4). Layout 1 is bound to the lane strip's selection, same as always; layouts 2 and 4 give each pane its own lane picker, independent of the strip. The chosen layout and each pane's lane persist to `localStorage` (`ccam.workspace.splitView`) across reloads.
 - **Lane grid** — one card per lane, 1 column, 2 at `md`, 3 at `xl`. Each card carries the lane id, liveness dot and status, title, declared stage with a progress bar and time-on-stage, the `auto:` chip when detection leads, the kind and CI tags, the working-copy facts from `GET /api/lanes/:id/git`, the needs-you banner, and the action row.
 
 Run history is per lane, queryable via `GET /api/run/history?laneId=<n>`.