ci: port workflows from .github/ to .forgejo/ (Forgejo Actions)

GitHub torrentclaw org is shadow-banned; CI is hosted at git.torrentclaw.com
now. Move workflows into the runner's natively-watched .forgejo/workflows/
tree and adapt steps to run in the available 'docker'-labeled Forgejo runner
without GitHub-only tooling (gh CLI, third-party marketplace actions).

- Use container: image to ship the toolchain (no actions/setup-* needed).
- Drop GitHub-only marketplace actions in favour of upstream installers
  invoked over curl/apt.
- Where a workflow created a GitHub Release (release.yml), substitute the
  step with a curl call against the Forgejo Releases API
  (POST /repos/<owner>/<repo>/releases).

.forgejo/workflows/ci.yml

@@ -12,17 +12,21 @@ permissions:
 jobs:
   test:
     name: Test
-    runs-on: ubuntu-latest
+    runs-on: docker
+    container:
+      image: docker.io/library/golang:1.24
     strategy:
       matrix:
         go-version: ["1.22", "1.23", "1.24"]
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: ${{ matrix.go-version }}
+      - name: Pin Go version (matrix override)
+        if: matrix.go-version != '1.24'
+        run: |
+          curl -sSL "https://go.dev/dl/go${{ matrix.go-version }}.linux-amd64.tar.gz" \
+            | tar -C /usr/local --strip-components=1 -xz
+          go version
 
       - name: Run tests
         run: go test -v -race -count=1 ./...
@@ -33,45 +37,35 @@ jobs:
           go test -race -coverprofile=coverage.out -covermode=atomic ./...
           COVERAGE=$(go tool cover -func=coverage.out | grep total | awk '{print $3}' | sed 's/%//')
           echo "Total coverage: ${COVERAGE}%"
+          apt-get update && apt-get install -y --no-install-recommends bc
           if [ "$(echo "$COVERAGE < 90" | bc)" -eq 1 ]; then
             echo "::error::Coverage ${COVERAGE}% is below 90% threshold"
             exit 1
           fi
 
-      - name: Upload coverage
-        if: matrix.go-version == '1.24'
-        uses: codecov/codecov-action@v4
-        with:
-          files: coverage.out
-        env:
-          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
-
   lint:
     name: Lint
-    runs-on: ubuntu-latest
+    runs-on: docker
+    container:
+      image: docker.io/library/golang:1.24
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: "1.24"
+      - name: Install golangci-lint
+        run: |
+          curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh \
+            | sh -s -- -b /usr/local/bin latest
 
       - name: Run golangci-lint
-        uses: golangci/golangci-lint-action@v6
-        with:
-          version: latest
+        run: golangci-lint run ./...
 
   vet:
     name: Vet
-    runs-on: ubuntu-latest
+    runs-on: docker
+    container:
+      image: docker.io/library/golang:1.24
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: "1.24"
-
       - name: Run go vet
         run: go vet ./...