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).

.github/workflows/ci.yml

@@ -1,77 +0,0 @@
-name: CI
-
-on:
-  push:
-    branches: [main]
-  pull_request:
-    branches: [main]
-
-permissions:
-  contents: read
-
-jobs:
-  test:
-    name: Test
-    runs-on: ubuntu-latest
-    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: ${{ matrix.go-version }}
-
-      - name: Run tests
-        run: go test -v -race -count=1 ./...
-
-      - name: Run tests with coverage
-        if: matrix.go-version == '1.24'
-        run: |
-          go test -race -coverprofile=coverage.out -covermode=atomic ./...
-          COVERAGE=$(go tool cover -func=coverage.out | grep total | awk '{print $3}' | sed 's/%//')
-          echo "Total coverage: ${COVERAGE}%"
-          if [ "$(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
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: "1.24"
-
-      - name: Run golangci-lint
-        uses: golangci/golangci-lint-action@v6
-        with:
-          version: latest
-
-  vet:
-    name: Vet
-    runs-on: ubuntu-latest
-    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 ./...