Add sops-nix secrets + dev defaults so local stack runs with zero setup

- sops-nix flake input, age + ssh-to-age in devShell, .sops.yaml with
  per-host recipients (real pubkeys still TODO until lars bootstraps).
- nix/modules/gebos-secrets.nix centralises per-host secret subsets and
  renders /run/secrets/gebos-env via sops.templates. Service modules now
  read EnvironmentFile= from services.gebos.secrets.envFile instead of
  the placeholder /etc/gebos/secrets.env.
- Falls back to a writeText env file when nix/secrets/secrets.yaml is
  absent, so `nix flake check` and first-boot eval work pre-bootstrap.
- nix/secrets/README.md walks through age key + sops bootstrap.
- Dev defaults: ingester binary falls back to local tcp/postgres URLs,
  process-compose adds mosquitto and wires GEBOS_MQTT_BROKER /
  GEBOS_POSTGRES_URL / GEBOS_POSTGRES_PASSWORD + VITE_SUPABASE_URL /
  VITE_SUPABASE_ANON_KEY, frontend defaults to 127.0.0.1:8000 in DEV.

Refs #23 (comment #110).

ingester/main.go

@@ -15,13 +15,34 @@ import (
 	"syscall"
 )
 
-func main() {
-	broker := os.Getenv("GEBOS_MQTT_BROKER")
-	pgURL := os.Getenv("GEBOS_POSTGRES_URL")
-	pgPassword := os.Getenv("GEBOS_POSTGRES_PASSWORD")
+// Defaults match the local dev stack in nix/dev/process-compose.nix so
+// `go run ./ingester` works without any env setup. Prod always sets these
+// explicitly via the systemd unit's EnvironmentFile.
+const (
+	defaultBroker     = "tcp://127.0.0.1:1883"
+	defaultPgURL      = "postgres://gebos_ingest@127.0.0.1:5432/gebos?sslmode=disable"
+	defaultPgPassword = "dev"
+)
 
-	if broker == "" || pgURL == "" || pgPassword == "" {
-		log.Fatal("GEBOS_MQTT_BROKER, GEBOS_POSTGRES_URL and GEBOS_POSTGRES_PASSWORD must be set")
+func envOr(key, fallback string) (string, bool) {
+	if v := os.Getenv(key); v != "" {
+		return v, false
+	}
+	return fallback, true
+}
+
+func main() {
+	broker, brokerDefault := envOr("GEBOS_MQTT_BROKER", defaultBroker)
+	pgURL, pgURLDefault := envOr("GEBOS_POSTGRES_URL", defaultPgURL)
+	pgPassword, pgPasswordDefault := envOr("GEBOS_POSTGRES_PASSWORD", defaultPgPassword)
+	_ = pgPassword
+
+	if brokerDefault || pgURLDefault || pgPasswordDefault {
+		log.Printf("gebos-ingester: using dev defaults for: %s%s%s — set env vars in prod",
+			ifStr(brokerDefault, "GEBOS_MQTT_BROKER ", ""),
+			ifStr(pgURLDefault, "GEBOS_POSTGRES_URL ", ""),
+			ifStr(pgPasswordDefault, "GEBOS_POSTGRES_PASSWORD ", ""),
+		)
 	}
 
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
@@ -35,7 +56,14 @@ func main() {
 	//   4. batch with a short flush interval (50–100ms) for throughput
 	//   5. shutdown on ctx.Done
 
-	log.Printf("gebos-ingester: broker=%s db=<redacted> (stub)", broker)
+	log.Printf("gebos-ingester: broker=%s db=%s (stub)", broker, pgURL)
 	<-ctx.Done()
 	log.Println("gebos-ingester: shutting down")
 }
+
+func ifStr(cond bool, a, b string) string {
+	if cond {
+		return a
+	}
+	return b
+}