chore(receiver): packaging, k8s manifests, CI/release, docs

Dockerfile.receiver (CGO-free, /data volume), receiver image in CI and
tag releases, receiver binary in release archives, make build-receiver,
example k8s manifests (deployment/service/ingress/secret/pvc) under
deploy/k8s/receiver/, and README coverage including sender/receiver
token pairing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -1,8 +1,8 @@
 name: Release
 
 # Builds release artifacts when a version tag (v*) is pushed:
-#   - cross-compiled CLI + server binaries attached to the Gitea release
-#   - version-tagged docker images for the CLI and web server
+#   - cross-compiled CLI + server + receiver binaries attached to the Gitea release
+#   - version-tagged docker images for the CLI, web server, and receiver
 # The owner usually creates the Gitea release by hand with notes; this
 # workflow attaches assets to it (creating a bare release only when none
 # exists) and skips assets that are already attached, so re-runs are safe.
@@ -42,10 +42,13 @@ jobs:
             CGO_ENABLED=0 GOOS="$GOOS" GOARCH="$GOARCH" \
               go build -trimpath -ldflags "-s -w -X main.version=${TAG}" \
               -o "${OUT}/exploredns-server${EXT}" ./cmd/server
+            CGO_ENABLED=0 GOOS="$GOOS" GOARCH="$GOARCH" \
+              go build -trimpath -ldflags "-s -w -X main.version=${TAG}" \
+              -o "${OUT}/exploredns-receiver${EXT}" ./cmd/exploredns-receiver
             if [ "$GOOS" = "windows" ]; then
-              (cd "$OUT" && zip -q "../exploredns_${TAG}_${GOOS}_${GOARCH}.zip" exploredns.exe exploredns-server.exe)
+              (cd "$OUT" && zip -q "../exploredns_${TAG}_${GOOS}_${GOARCH}.zip" exploredns.exe exploredns-server.exe exploredns-receiver.exe)
             else
-              tar -czf "dist/exploredns_${TAG}_${GOOS}_${GOARCH}.tar.gz" -C "$OUT" exploredns exploredns-server
+              tar -czf "dist/exploredns_${TAG}_${GOOS}_${GOARCH}.tar.gz" -C "$OUT" exploredns exploredns-server exploredns-receiver
             fi
             rm -rf "$OUT"
           done
@@ -130,3 +133,15 @@ jobs:
           tags: |
             gitea.hansenits.com.au/hits/exploredns-web:latest
             gitea.hansenits.com.au/hits/exploredns-web:${{ github.ref_name }}
+
+      - name: Build and push receiver image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: Dockerfile.receiver
+          push: true
+          build-args: |
+            VERSION=${{ github.ref_name }}
+          tags: |
+            gitea.hansenits.com.au/hits/exploredns-receiver:latest
+            gitea.hansenits.com.au/hits/exploredns-receiver:${{ github.ref_name }}