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/favicon.ico/route.js

@@ -0,0 +1,6 @@
+var R=require("../../chunks/[turbopack]_runtime.js")("server/app/favicon.ico/route.js")
+R.c("server/chunks/[root-of-the-server]__009pdeo._.js")
+R.c("server/chunks/[root-of-the-server]__0j8-xkl._.js")
+R.c("server/chunks/_next-internal_server_app_favicon_ico_route_actions_095lj93.js")
+R.m(88165)
+module.exports=R.m(88165).exports