refactor(api): separate Yggdrasil routes from v1 API group

Move Yggdrasil API endpoints from /api/v1/yggdrasil to /api/yggdrasil for
better route organization and compatibility with standard Yggdrasil protocol.
Also upgrade Go to 1.25, update dependencies, and migrate email package from
jordan-wright/email to gopkg.in/mail.v2. Remove deprecated UUID design plan.

.gitea/workflows/build.yml

@@ -32,6 +32,7 @@ jobs:
           GOOS: linux
           GOARCH: amd64
           CGO_ENABLED: 0
+          GOEXPERIMENT: greenteagc
         run: go build -v -o mcauth-linux-amd64 ./cmd/server
 
       - name: Upload artifacts