feat(workspace): session view console as tabs, with New terminal

The 1/2/4 split view becomes a tab bar (ConsoleTabs.tsx): one tab per live
tmux slot (0-3) of the workspace, the active one being ?run=, every live tab's
pane kept mounted and hidden with CSS. The + menu opens a new tab in the first
free slot: New terminal (a plain shell - shell: true on POST
/api/lanes/:id/start, spawnShell, tool 'shell', no run_id/status change), any
installed enabled AI tool started bare, or Settings -> Agents. A tab's x stops
its session. splitViewStorage, &pane= and the sidebar's Ctrl/Cmd+click are gone.

client/src/lib/laneOrderStorage.ts

@@ -1,11 +1,10 @@
 /**
  * @file laneOrderStorage.ts
  * @description Persists the Workspace lane strip's user-chosen card order to
- * localStorage, the same read/validate/fallback convention as
- * splitViewStorage.ts.
+ * localStorage, the same read/validate/fallback convention as useTheme.ts.
  *
  * The order lives in the browser rather than the lanes table on purpose: it is
- * a per-viewer preference, like the split-pane layout beside it, and nothing
+ * a per-viewer preference, and nothing
  * server-side (the CLI's `agenthub lanes`, the pipeline-stats picker) has an
  * opinion about it. Ceiling: the order does not follow the user to another
  * browser or to the CLI — move it to a `lanes.sort_order` column if it ever