chore(agent): add CHANGELOG, version the agent at 0.1.0

- CHANGELOG.md with the v0.1.0 (slice 1) entry
- main: version var (0.1.0, ldflags-overridable) + --version flag; version shown
  in selftest header and startup log

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/felhom-agent/main.go

@@ -22,17 +22,28 @@ import (
 	"gitea.dooplex.hu/admin/felhom-agent/internal/proxmox"
 )
 
+// version is the agent version. Overridable at build time with
+// -ldflags "-X main.version=<v>"; defaults to the in-repo CHANGELOG version.
+var version = "0.1.0"
+
 func main() {
 	var (
-		cfgPath  string
-		selftest selftestFlag
-		vmid     int
+		cfgPath     string
+		selftest    selftestFlag
+		vmid        int
+		showVersion bool
 	)
 	flag.StringVar(&cfgPath, "config", envOr("FELHOM_AGENT_CONFIG", "/etc/felhom-agent/agent.json"), "path to the agent config file (JSON)")
 	flag.Var(&selftest, "selftest", "run a self-test and exit: bare/`read` = read-only queries; `task` = reversible mutating exercise (needs -vmid)")
 	flag.IntVar(&vmid, "vmid", 0, "guest VMID for --selftest=task (the reversible snapshot/rollback exercise)")
+	flag.BoolVar(&showVersion, "version", false, "print version and exit")
 	flag.Parse()
 
+	if showVersion {
+		fmt.Println("felhom-agent", version)
+		return
+	}
+
 	cfg, err := config.Load(cfgPath)
 	if err != nil {
 		// A missing default config file is fine if env provides the values; only a
@@ -48,7 +59,8 @@ func main() {
 	switch selftest.mode {
 	case "":
 		// No daemon loop yet.
-		logger.Info("felhom-agent slice-1 scaffold; no run loop yet",
+		logger.Info("felhom-agent scaffold; no run loop yet",
+			"version", version,
 			"hint", "use --selftest (read-only) or --selftest=task --vmid N")
 		// TODO: poll loop — slice 3/4.
 		return
@@ -87,7 +99,7 @@ func runSelftestRead(ctx context.Context, cfg config.Config, logger *slog.Logger
 	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
 	defer cancel()
 
-	fmt.Println("=== felhom-agent selftest (read-only) ===")
+	fmt.Printf("=== felhom-agent %s selftest (read-only) ===\n", version)
 	fmt.Printf("endpoint : %s  node=%s\n", cfg.Proxmox.Endpoint, cfg.Proxmox.Node)
 
 	fail := 0