fix(lanes): stop archive/activate from clobbering feature title and links

archiveActiveFeature was overwriting a feature's own title with the
LIVE lane's title on every clear/switch — a --title set on activation
silently disappeared. activateFeature restored stage/status/gate/CI/
stages/notes onto the live lane when switching back to a past feature,
but never links, so they vanished on reactivation. Both are fixed, with
a regression test for each (full activate/archive/reactivate round trip
for links).

Also fixes server/routes/lanes.js: the doc comment explaining GET
/:id/git's rationale had been left sitting above the newly-inserted
/:id/features routes instead of its own route.

docs/API.md's Lane features section described fields and behavior that
don't exist in the real routes (an "active" boolean, a POST response
containing "archivedPrevious", a "409 ESTALE" concurrency response) —
rewritten to match the actual request/response shapes exactly.

server/routes/lanes.js

@@ -239,19 +239,11 @@ router.get("/:id/preflight", async (req, res) => {
 });
 
 /**
- * A lane's working-copy facts: branch, short HEAD, that commit's subject, and
- * the uncommitted counts. Read-only, so no same-origin guard — that guard
- * exists for the destructive actions.
- *
- * Deliberately NOT part of `GET /api/lanes`: this shells out to git three
- * times, and that payload is polled and re-broadcast on every hook-driven
- * lane_update. Any failure — no such directory, not a repo, git itself
- * erroring — is reported as `available: false` rather than a 500, because a
- * lane pointing at a plain directory is a normal state, not a fault.
- *
- * The `/:id/:action` catch-all below cannot shadow this one — that route is a
- * POST and Express matches on method as well as path. Verified by moving this
- * registration after it: the suite stayed green.
+ * Per-feature state and archive (B) — `lib/lane-features.js`. `GET
+ * /:id/features` lists every feature the lane has ever activated (archived
+ * or live); `GET /:id/features/:slug` shows one, including an archived
+ * one's saved pipeline; `POST /:id/features/activate` switches the live
+ * lane to a feature by slug, archiving whichever one was active first.
  */
 router.get("/:id/features", (req, res) => {
   const lane = lanesLib.getLane(req.params.id);
@@ -290,6 +282,21 @@ router.post("/:id/features/activate", sameOriginGuard, (req, res) => {
   }
 });
 
+/**
+ * A lane's working-copy facts: branch, short HEAD, that commit's subject, and
+ * the uncommitted counts. Read-only, so no same-origin guard — that guard
+ * exists for the destructive actions.
+ *
+ * Deliberately NOT part of `GET /api/lanes`: this shells out to git three
+ * times, and that payload is polled and re-broadcast on every hook-driven
+ * lane_update. Any failure — no such directory, not a repo, git itself
+ * erroring — is reported as `available: false` rather than a 500, because a
+ * lane pointing at a plain directory is a normal state, not a fault.
+ *
+ * The `/:id/:action` catch-all below cannot shadow this one — that route is a
+ * POST and Express matches on method as well as path. Verified by moving this
+ * registration after it: the suite stayed green.
+ */
 router.get("/:id/git", async (req, res) => {
   const lane = lanesLib.getLane(req.params.id);
   if (!lane) return res.status(404).json({ error: { code: "ENOLANE", message: "lane not found" } });