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`.

server/routes/lanes.js

@@ -161,11 +161,15 @@ router.post("/ensure", sameOriginGuard, (req, res) => {
   const owner = lanesLib.resolveLaneByCwd(body.cwd);
   if (owner) return res.json({ lane: payload(owner), created: false });
   try {
-    const lane = lanesLib.createLane({ cwd: body.cwd, title: body.title || "" });
+    const lane = lanesLib.createLane({
+      cwd: body.cwd,
+      title: body.title || "",
+      ...(body.pipeline ? { pipeline: body.pipeline } : {}),
+    });
     broadcastLane(lane.id);
     return res.status(201).json({ lane: payload(lane), created: true });
   } catch (err) {
-    if (err.code === "EBADCWD") {
+    if (err.code === "EBADCWD" || err.code === "EBADPIPELINE") {
       return res.status(400).json({ error: { code: err.code, message: err.message } });
     }
     // The cwd UNIQUE constraint is the arbiter: someone else won the race, so
@@ -248,7 +252,7 @@ router.post("/", sameOriginGuard, (req, res) => {
     broadcastLane(lane.id);
     res.status(201).json({ lane: payload(lane) });
   } catch (err) {
-    if (err.code === "EBADCWD") {
+    if (err.code === "EBADCWD" || err.code === "EBADPIPELINE" || err.code === "EBADKIND") {
       return res.status(400).json({ error: { code: err.code, message: err.message } });
     }
     if (err.code === "SQLITE_CONSTRAINT_UNIQUE" || String(err.message).includes("UNIQUE")) {
@@ -569,6 +573,7 @@ router.post("/worktree", sameOriginGuard, async (req, res) => {
       source_repo: resolvedSourceRepo,
       base_branch: body.base || null,
       slug,
+      ...(body.pipeline ? { pipeline: body.pipeline } : {}),
     });
     lane = lanesLib.updateLane(lane.id, { status: "provisioning" });
   } catch (err) {