fix: stop .gitignore from excluding build/.next (site 502/blank after deploy)

.gitignore's ".next/" rule (no leading slash) matched at any depth, so
build/.next was silently excluded from every commit even though build.sh
populates it. The Docker image was built without the compiled server/static
output, so server.js had nothing to serve. Anchor the rule to the repo root
and commit the compiled output that Dokploy actually needs.

build/.next/server/app/air-freight/page/next-font-manifest.json

@@ -0,0 +1,14 @@
+{
+  "pages": {},
+  "app": {
+    "[project]/src/app/air-freight/page": [
+      "static/media/a343f882a40d2cc9-s.p.0kho-wj7-y-w1.woff2",
+      "static/media/0c89a48fa5027cee-s.p.0rd3rjvnnhw7n.woff2",
+      "static/media/0c795a286deabae8-s.p.14tvuu96~wkr0.woff2",
+      "static/media/5c285b27cdda1fe8-s.p.0yo6-5yoeeudq.woff2",
+      "static/media/83afe278b6a6bb3c-s.p.0q-301v4kxxnr.woff2"
+    ]
+  },
+  "appUsingSizeAdjust": true,
+  "pagesUsingSizeAdjust": false
+}