feat(lanes): extract skills-install lib, add POST /api/skills/install (F4)

server/lib/skills-install.js

@@ -0,0 +1,32 @@
+/**
+ * @file Installs .claude/skills/ship-feature-lane/ into ~/.claude/skills/, so
+ * /ship-feature-lane is discoverable from a session running inside any
+ * lane's own working directory — not just inside this repo, where it lives
+ * until installed. Shared by bin/ccam.js's `ccam skills install` CLI and the
+ * POST /api/skills/install route, so there is exactly one copy of this
+ * logic. Pure filesystem action.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+
+/**
+ * @param {{repoRoot: string}} options - `repoRoot` is this checkout's own
+ *   root (bin/ccam.js already computes this as `REPO_ROOT`; the server
+ *   computes its own equivalent — see the route for how).
+ * @returns {{installed: true, path: string}}
+ */
+function installShipFeatureLaneSkill({ repoRoot }) {
+  const src = path.join(repoRoot, ".claude", "skills", "ship-feature-lane");
+  if (!fs.existsSync(src)) {
+    throw Object.assign(new Error(`not found: ${src}`), { code: "ENOSKILLSRC" });
+  }
+  const dest = path.join(os.homedir(), ".claude", "skills", "ship-feature-lane");
+  fs.mkdirSync(path.dirname(dest), { recursive: true });
+  fs.cpSync(src, dest, { recursive: true, force: true });
+  return { installed: true, path: dest };
+}
+
+module.exports = { installShipFeatureLaneSkill };