feat(lanes): let Add Lane choose the pipeline template

Creation is the only point the UI could ever set a lane's template, and it
never offered the choice — so every lane added from "+ Add lane" was born
on `default` and rendered an 8-node map for a 16-node workflow, with no
screen able to change it afterwards. That is the defect that made the
ship-feature template unreachable from the browser.

The modal now shows a *Pipeline template* select fed by
`GET /api/lanes/pipelines`, labelled with each template's node count so the
consequence of the choice is visible. A failed fetch degrades to a `default`
option rather than blocking lane creation.

`pipeline` was already accepted by `POST /api/lanes` but silently dropped by
`/ensure` and `/worktree`, which build their own createLane payloads; both
now pass it through, and both map `EBADPIPELINE` to 400 like `EBADCWD`.

client/src/components/lanes/AddLaneModal.tsx

@@ -92,6 +92,8 @@ export function AddLaneModal({
   const [branch, setBranch] = useState("");
   const [branches, setBranches] = useState<string[] | null>(null);
   const [base, setBase] = useState("");
+  const [pipeline, setPipeline] = useState("default");
+  const [pipelines, setPipelines] = useState<{ id: string; name: string; nodes: unknown[] }[]>([]);
   const [branchesError, setBranchesError] = useState<string | null>(null);
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
@@ -109,12 +111,35 @@ export function AddLaneModal({
     setBranch("");
     setBranches(null);
     setBase("");
+    setPipeline("default");
     setBranchesError(null);
     setError(null);
     setBusy(false);
     setSetupResult(null);
   };
 
+  // The template a lane is created with is the ONLY chance to get it right
+  // from here: nothing else in the UI can change it afterwards, so a lane
+  // silently born on `default` renders an 8-node map for a 16-node workflow.
+  // Fetched on open (templates are file-backed and can change between opens).
+  useEffect(() => {
+    if (!open) return;
+    let cancelled = false;
+    api.lanes
+      .pipelines()
+      .then((r) => {
+        if (!cancelled) setPipelines(r.pipelines);
+      })
+      .catch(() => {
+        // Quiet: the select just falls back to the single `default` option
+        // below, and the lane still gets created.
+        if (!cancelled) setPipelines([]);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [open]);
+
   // Look up the repo's branches once the path settles - debounced so every
   // keystroke while typing a path doesn't fire a request against a path that
   // isn't finished yet. Worktree mode only: "Repo" mode adopts as-is and
@@ -158,7 +183,11 @@ export function AddLaneModal({
 
     if (mode === "repo") {
       try {
-        const result = await api.lanes.ensure({ cwd: repo, title: name || undefined });
+        const result = await api.lanes.ensure({
+          cwd: repo,
+          title: name || undefined,
+          pipeline,
+        });
         onAdded(result.lane);
         reset();
         onClose();
@@ -176,6 +205,7 @@ export function AddLaneModal({
         title: name,
         base: base || undefined,
         branch: branch.trim(),
+        pipeline,
       });
       onAdded(result.lane);
 
@@ -318,6 +348,27 @@ export function AddLaneModal({
           />
         </div>
 
+        <div>
+          <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-pipeline">
+            {t("addLanePipelineLabel")}
+          </label>
+          <select
+            id="add-lane-pipeline"
+            value={pipeline}
+            onChange={(e) => setPipeline(e.target.value)}
+            className="w-full rounded-md border border-border-light bg-surface-0 px-3 py-1.5 text-xs text-fg-primary focus:border-blue-500 focus:outline-none"
+          >
+            {(pipelines.length ? pipelines : [{ id: "default", name: "default", nodes: [] }]).map(
+              (p) => (
+                <option key={p.id} value={p.id}>
+                  {p.nodes.length ? `${p.name} (${p.nodes.length})` : p.name}
+                </option>
+              )
+            )}
+          </select>
+          <p className="mt-1 text-[10px] text-fg-muted">{t("addLanePipelineHint")}</p>
+        </div>
+
         {mode === "worktree" && branches && (
           <div>
             <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-base">