Stage 1: project skeleton, SQLite, migrations, HTTP server

- go mod init with chi, modernc.org/sqlite, golang.org/x/crypto
- Custom embedded migration runner (no CGO dependency)
- Config from TERDUT_ADDR / TERDUT_DB_PATH env vars
- chi router with /healthz endpoint
- Graceful shutdown on SIGINT/SIGTERM

internal/db/db.go

@@ -0,0 +1,79 @@
+package db
+
+import (
+	"database/sql"
+	"embed"
+	"fmt"
+	"io/fs"
+	"sort"
+	"strings"
+
+	_ "modernc.org/sqlite"
+)
+
+//go:embed migrations
+var migrationsFS embed.FS
+
+func Open(path string) (*sql.DB, error) {
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, err
+	}
+	// SQLite does not support concurrent writers; a single connection avoids locking errors.
+	db.SetMaxOpenConns(1)
+	if _, err := db.Exec("PRAGMA journal_mode=WAL; PRAGMA foreign_keys=ON;"); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("set pragmas: %w", err)
+	}
+	if err := db.Ping(); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("ping: %w", err)
+	}
+	return db, nil
+}
+
+func Migrate(db *sql.DB) error {
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
+		version    TEXT PRIMARY KEY,
+		applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
+	)`); err != nil {
+		return fmt.Errorf("create schema_migrations: %w", err)
+	}
+
+	entries, err := fs.ReadDir(migrationsFS, "migrations")
+	if err != nil {
+		return fmt.Errorf("read migrations dir: %w", err)
+	}
+
+	var files []string
+	for _, e := range entries {
+		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
+			files = append(files, e.Name())
+		}
+	}
+	sort.Strings(files)
+
+	for _, name := range files {
+		var count int
+		if err := db.QueryRow("SELECT COUNT(*) FROM schema_migrations WHERE version = ?", name).Scan(&count); err != nil {
+			return fmt.Errorf("check migration %s: %w", name, err)
+		}
+		if count > 0 {
+			continue
+		}
+
+		data, err := migrationsFS.ReadFile("migrations/" + name)
+		if err != nil {
+			return fmt.Errorf("read migration %s: %w", name, err)
+		}
+
+		if _, err := db.Exec(string(data)); err != nil {
+			return fmt.Errorf("apply migration %s: %w", name, err)
+		}
+
+		if _, err := db.Exec("INSERT INTO schema_migrations (version) VALUES (?)", name); err != nil {
+			return fmt.Errorf("record migration %s: %w", name, err)
+		}
+	}
+	return nil
+}