Implement Phase 1: core framework, operational tooling, and runbook

Core packages: crypto (Argon2id/AES-256-GCM), config (TOML/viper),
db (SQLite/migrations), barrier (encrypted storage), seal (state machine
with rate-limited unseal), auth (MCIAS integration with token cache),
policy (priority-based ACL engine), engine (interface + registry).

Server: HTTPS with TLS 1.2+, REST API, auth/admin middleware, htmx web UI
(init, unseal, login, dashboard pages).

CLI: cobra/viper subcommands (server, init, status, snapshot) with env
var override support (METACRYPT_ prefix).

Operational tooling: Dockerfile (multi-stage, non-root), docker-compose,
hardened systemd units (service + daily backup timer), install script,
backup script with retention pruning, production config examples.

Runbook covering installation, configuration, daily operations,
backup/restore, monitoring, troubleshooting, and security procedures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/db/db.go

@@ -0,0 +1,43 @@
+// Package db provides SQLite database access and migrations.
+package db
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+
+	_ "modernc.org/sqlite"
+)
+
+// Open opens or creates a SQLite database at the given path with secure
+// file permissions (0600) and WAL mode enabled.
+func Open(path string) (*sql.DB, error) {
+	// Ensure the file has restrictive permissions if it doesn't exist yet.
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0600)
+		if err != nil {
+			return nil, fmt.Errorf("db: create file: %w", err)
+		}
+		f.Close()
+	}
+
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, fmt.Errorf("db: open: %w", err)
+	}
+
+	// Enable WAL mode and foreign keys.
+	pragmas := []string{
+		"PRAGMA journal_mode=WAL",
+		"PRAGMA foreign_keys=ON",
+		"PRAGMA busy_timeout=5000",
+	}
+	for _, p := range pragmas {
+		if _, err := db.Exec(p); err != nil {
+			db.Close()
+			return nil, fmt.Errorf("db: pragma %q: %w", p, err)
+		}
+	}
+
+	return db, nil
+}