ci: migrate workflows to Gitea Actions with self-hosted runner

Replaced GitHub Actions with Gitea-compatible workflows:
- CI: build + test + vet on ubuntu-latest (self-hosted runner)
- Release: cross-compile 6 binaries (linux/darwin/windows x amd64/arm64)
  with Gitea API release creation and asset uploads
- Removed .github/workflows in favor of .gitea/workflows

Requires Gitea secrets: GITEA_TOKEN, GITEA_SERVER, GITEA_REPO

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

.gitea/workflows/ci.yml

@@ -0,0 +1,31 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Go
+        run: |
+          wget -q https://go.dev/dl/go1.24.3.linux-amd64.tar.gz
+          sudo rm -rf /usr/local/go
+          sudo tar -C /usr/local -xzf go1.24.3.linux-amd64.tar.gz
+          export PATH=/usr/local/go/bin:$PATH
+          echo "PATH=/usr/local/go/bin:$PATH" >> $GITHUB_ENV
+          go version
+
+      - name: Build
+        run: go build -o muyue ./cmd/muyue/
+
+      - name: Test
+        run: go test ./... -v
+
+      - name: Vet
+        run: go vet ./...