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>

README.md

@@ -0,0 +1,70 @@
+# nasmon
+
+Lightweight NAS health monitor written in Go. Web dashboard (CPU, memory
+incl. ZFS ARC, temperatures, physical disks with SMART, ZFS pools and
+datasets) with periodic SMART/ZFS checks and e-mail alerts, plus SMB/NFS
+share management from the UI.
+
+* Web UI: `http://<host>:8090`
+* Settings: `http://<host>:8090/settings` (also `/etc/nasmon/config.json`)
+* State: `/var/lib/nasmon/nasmon.db` (SMART history, alert log)
+* Service: `systemctl status nasmon` / `journalctl -u nasmon -f`
+* JSON API: `/api/status`, `/api/history?hours=24`, `/api/disks/<serial>/history?days=30`
+
+No authentication — designed for a LAN-only NAS (the `/shares` page can
+create SMB/NFS users and exports, so keep it off the public internet).
+
+See [packaging/README.md](packaging/README.md) for the full operational
+doc (ZFS dataset management, SMB/NFS shares, alert lifecycle) — it ships
+inside the package as `/usr/share/doc/nasmon/README.md`.
+
+## Build
+
+Go 1.22, [nfpm](https://nfpm.goreleaser.com/) (no `rpmbuild`/`dpkg-deb`
+needed — nfpm builds both formats natively).
+
+```powershell
+# Windows
+.\build.ps1                # dist\nasmon_<version>_amd64.deb + dist\nasmon-<version>.x86_64.rpm
+.\build.ps1 -Test          # go vet + go test first
+.\build.ps1 -Version 0.2.0
+```
+
+```bash
+# Linux/WSL/CI
+./build.sh
+TEST=1 ./build.sh
+VERSION=0.2.0 ./build.sh
+```
+
+One-time tool setup:
+
+```
+go install github.com/goreleaser/nfpm/v2/cmd/nfpm@latest
+```
+
+## Packaging
+
+`packaging/nfpm.yaml` builds both formats from one spec:
+
+- **.deb** (Ubuntu/Debian): depends on `smartmontools`, `zfsutils-linux`, `util-linux`;
+  recommends `samba`, `nfs-kernel-server`, `wsdd` for the `/shares` page.
+- **.rpm** (Fedora/RHEL/Rocky, `dnf`): depends on `smartmontools`, `util-linux`;
+  recommends `samba`, `nfs-utils`, `wsdd`. ZFS is **not** a hard dependency on
+  rpm — RHEL-family distros have no native ZFS package; install the
+  [OpenZFS](https://openzfs.github.io/openzfs-docs/Getting%20Started/RHEL-based%20distro/index.html)
+  repo yourself if you need the `/zfs` page's pool/dataset features.
+
+Both formats install the same systemd unit (`packaging/nasmon.service`, run
+as root — it needs `smartctl`/`zpool`), just at their respective conventional
+paths (`/lib/systemd/system` on deb, `/usr/lib/systemd/system` on rpm), plus
+the bundled `wsdd.service` unit (Ubuntu/Fedora `wsdd` packages ship no unit
+of their own), default config at `/etc/nasmon/config.json`, and
+`postinst.sh`/`prerm.sh`/`postrm.sh` maintainer scripts (written to run
+correctly under both dpkg and rpm argument conventions).
+
+## CI
+
+`.gitea/workflows/build.yml` runs `go vet`/`go test` and builds both
+packages on every push, uploading `dist/*.deb` and `dist/*.rpm` as build
+artifacts.