Initial import: nasmon health monitor, split out of home_nas

Go service (nasmon/) plus nfpm packaging (packaging/), carried over from
the home_nas monorepo. Adds rpm packaging alongside the existing deb
build (Fedora/RHEL/Rocky dependency names via nfpm overrides, per-format
systemd unit path, dpkg+rpm-compatible maintainer scripts) and a Gitea
Actions workflow that builds both formats on every push.

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

.gitea/workflows/build.yml

@@ -0,0 +1,37 @@
+name: build
+
+on:
+  push:
+    branches: ["**"]
+    tags: ["v*"]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.22"
+
+      - name: vet & test
+        run: |
+          go vet ./...
+          go test ./...
+
+      - name: install nfpm
+        run: go install github.com/goreleaser/nfpm/v2/cmd/nfpm@latest
+
+      - name: build packages
+        run: |
+          export PATH="$PATH:$(go env GOPATH)/bin"
+          ./build.sh
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: nasmon-packages
+          path: |
+            dist/*.deb
+            dist/*.rpm