ci: migrate release pipeline from Woodpecker to GitHub Actions

Drop the broken .woodpecker/release.yml (top-level when: triggered an
'error' status on every dev push instead of skipping non-tag events)
and replace with .github/workflows/release.yml driving the same
GoReleaser flow.

Rationale:
- Release artifacts already land on GitHub (releases + ghcr.io), so
  running the pipeline on GitHub eliminates a build hop.
- GH Actions auto-provides GITHUB_TOKEN with packages:write via the
  workflow permissions block — no PAT plumbing or login secrets.
- docker/setup-qemu-action and docker/setup-buildx-action handle the
  multi-arch cross-build setup that Woodpecker would require manual
  host configuration for.

Trigger: any tag matching refs/tags/v*. Mirror sync from somegit.dev
propagates tags to GitHub, so 'git push origin v0.3.1' on the canonical
remote still drives the GitHub-side release.

.github/workflows/release.yml

@@ -0,0 +1,63 @@
+# Release workflow — runs when a vX.Y.Z tag is pushed (including mirror
+# pushes from somegit.dev). Drives GoReleaser to publish:
+#   - static binaries (linux/darwin/windows × amd64/arm64) + checksums
+#     + autogenerated changelog to the GitHub releases page
+#   - multi-arch container images to ghcr.io/vikingowl91/gnoma
+#
+# GITHUB_TOKEN is provided automatically by GitHub Actions and already
+# carries packages:write thanks to the permissions block, so no PAT is
+# needed for either the release upload or the ghcr.io push.
+#
+# Security note: this workflow does not interpolate any untrusted
+# context (commit messages, PR titles, issue bodies) into shell commands.
+# All ${{ ... }} references live in with: / env: blocks, which are
+# safely passed as strings rather than evaluated as shell.
+
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: write
+  packages: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.26"
+
+      - name: Setup QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Test
+        run: go test ./...
+
+      - name: GoReleaser
+        uses: goreleaser/goreleaser-action@v6
+        with:
+          version: latest
+          args: release --clean
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}