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.

server/__tests__/lanes-api.test.js

@@ -401,6 +401,42 @@ describe("lane start input", () => {
       fs.rmSync(cwd, { recursive: true, force: true });
     }
   });
+
+  // A Terminal tab: the user's own shell in the workspace folder, no AI tool —
+  // so it is no agent at work and leaves the lane's run_id/status alone.
+  it("opens a plain shell for `shell: true`, without marking the lane running", async () => {
+    const tmux = require("../lib/tmux");
+    const cwd = fs.mkdtempSync(path.join(os.tmpdir(), "lane-shell-"));
+    const id = (await request("POST", "/api/lanes", { cwd })).body.lane.id;
+    let created = null;
+    try {
+      tmux.__setExecImpl((args) => {
+        if (args[0] === "has-session" && !created) throw new Error("no such session");
+        if (args[0] === "new-session") created = args;
+        return "";
+      });
+      const r = await request("POST", `/api/lanes/${id}/start`, {
+        slot: 1,
+        shell: true,
+        prompt: "ignored",
+        tool: "codex",
+      });
+      assert.equal(r.status, 200);
+      assert.equal(r.body.run_id, `agenthub-lane-${id}-1`);
+      assert.equal(created[created.indexOf("-s") + 1], `agenthub-lane-${id}-1`);
+      assert.equal(created[created.indexOf("-c") + 1], cwd);
+      // Nothing after `--`: tmux runs the user's own default shell.
+      assert.equal(created[created.length - 1], "--");
+      const lane = (await request("GET", `/api/lanes/${id}`)).body.lane;
+      assert.equal(lane.run_id, null);
+      assert.notEqual(lane.status, "running");
+      const run = (await request("GET", `/api/run/agenthub-lane-${id}-1`)).body;
+      assert.equal(run.tool, "shell");
+    } finally {
+      tmux.__reset();
+      fs.rmSync(cwd, { recursive: true, force: true });
+    }
+  });
 });
 
 describe("hook → lane binding", () => {