ci: add Gitea Actions — CI on push/PR, release on version tags

- .gitea/workflows/ci.yml: build + test on every push and PR
- .gitea/workflows/release.yml: cross-platform release binaries on v*.*.* tags
  - Builds amcs-server and amcs-cli for linux/amd64, linux/arm64, darwin/amd64, darwin/arm64, windows/amd64
  - Embeds version, commit, and build date via ldflags
  - Creates Gitea Release with all binaries and checksums.txt attached

.gitea/workflows/ci.yml

@@ -0,0 +1,41 @@
+name: CI
+
+on:
+  push:
+    branches: ['**']
+    tags-ignore: ['v*']
+  pull_request:
+    branches: ['**']
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.26'
+
+      - name: Cache Go modules
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-go-
+
+      - name: Download dependencies
+        run: go mod download
+
+      - name: Run tests
+        run: go test ./...
+
+      - name: Build amcs-server
+        run: go build -o /dev/null ./cmd/amcs-server
+
+      - name: Build amcs-cli
+        run: go build -o /dev/null ./cmd/amcs-cli