core: initial Go module skeleton (config, db pool, tenant registry migration)

.gitignore

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+*.log
+.env

DEVLOG.md

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+# code – Dev Log
+
+## 2026-08-27 17:17 – 17:18 (0m)
+**Beschreibung:** Claude Code Session
+**Projekt:** nexarch
+
+### Commits
+Keine Commits in dieser Session.
+
+### Geänderte Dateien
+Keine Änderungen ermittelbar.
+
+---
+## 2026-08-27 17:21 – 17:21 (0m)
+**Beschreibung:** Claude Code Session
+**Projekt:** code
+
+### Commits
+Keine Commits in dieser Session.
+
+### Geänderte Dateien
+Keine Änderungen ermittelbar.
+
+---
+## 2026-08-27 17:22 – 17:22 (0m)
+**Beschreibung:** Claude Code Session
+**Projekt:** code
+
+### Commits
+Keine Commits in dieser Session.
+
+### Geänderte Dateien
+Keine Änderungen ermittelbar.
+
+---
+## 2026-08-27 17:23 – 17:25 (2m)
+**Beschreibung:** Claude Code Session
+**Projekt:** code
+
+### Commits
+Keine Commits in dieser Session.
+
+### Geänderte Dateien
+Keine Änderungen ermittelbar.
+
+---

cmd/core/main.go

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+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+
+	"gitea.perlbach24.de/scripte/nexarch/internal/config"
+	"gitea.perlbach24.de/scripte/nexarch/internal/db"
+)
+
+func main() {
+	cfg, err := config.Load()
+	if err != nil {
+		log.Fatalf("config: %v", err)
+	}
+
+	pool, err := db.Connect(context.Background(), cfg.RegistryDSN)
+	if err != nil {
+		log.Fatalf("db: %v", err)
+	}
+	defer pool.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+
+	log.Printf("nexarch-core listening on %s", cfg.ListenAddr)
+	if err := http.ListenAndServe(cfg.ListenAddr, mux); err != nil {
+		log.Fatalf("server: %v", err)
+	}
+}

go.mod

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+module gitea.perlbach24.de/scripte/nexarch
+
+go 1.22
+
+require github.com/jackc/pgx/v5 v5.6.0

internal/config/config.go

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+package config
+
+import (
+	"fmt"
+	"os"
+)
+
+// Config holds startup configuration for the core module.
+// RegistryDSN points at the control-plane registry DB (tenant list,
+// connection info, superadmin accounts) — see nexarch-state.json
+// multi_tenancy: Modell C (physisch getrennte DB pro Mandant).
+type Config struct {
+	ListenAddr  string
+	RegistryDSN string
+}
+
+func Load() (Config, error) {
+	dsn := os.Getenv("NEXARCH_REGISTRY_DSN")
+	if dsn == "" {
+		return Config{}, fmt.Errorf("NEXARCH_REGISTRY_DSN not set")
+	}
+
+	addr := os.Getenv("NEXARCH_LISTEN_ADDR")
+	if addr == "" {
+		addr = ":8080"
+	}
+
+	return Config{ListenAddr: addr, RegistryDSN: dsn}, nil
+}

internal/db/db.go

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+package db
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+func Connect(ctx context.Context, dsn string) (*pgxpool.Pool, error) {
+	return pgxpool.New(ctx, dsn)
+}

migrations/0001_tenant_registry.sql

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+-- Control-plane registry: tenant list + connection info (Modell C).
+-- Core TEN-01 (siehe core-kanban).
+CREATE TABLE tenants (
+    id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    slug         TEXT NOT NULL UNIQUE,
+    name         TEXT NOT NULL,
+    db_dsn       TEXT NOT NULL,
+    status       TEXT NOT NULL DEFAULT 'active',
+    created_at   TIMESTAMPTZ NOT NULL DEFAULT now()
+);