feat(server): скелет Go-сервера с healthz, readyz и api/v1/meta

- internal/config: конфигурация из env с валидацией и дефолтами (§5.1, §9.1)
- internal/httpx: middleware (request id, slog-логи, recover, security-заголовки),
  единый формат ошибок §8.5 и лимит тела запроса
- internal/database: SQLite WAL + busy_timeout + foreign_keys, один writer
  и пул чтения, goose-миграции embedded, PRAGMA optimize по расписанию
- internal/meta: полезная нагрузка /api/v1/meta (версия, фичи, лимиты)
- internal/server: маршруты, SPA-раздача собранного клиента, OpenAPI 3.1
- cmd/glchat: точка входа с graceful shutdown и JSON-логами
- тесты: конфиг, миграции и идемпотентность, HTTP-эндпоинты, статика, 404/405

internal/config/config.go

@@ -0,0 +1,132 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	DefaultListenAddr = "127.0.0.1:8080"
+	DefaultDataDir    = "/opt/glchat/data"
+	DefaultLogLevel   = "info"
+)
+
+type Config struct {
+	Domain        string
+	FilesDomain   string
+	InstanceName  string
+	ListenAddr    string
+	DataDir       string
+	WebRoot       string
+	DatabasePath  string
+	SQLiteCache   string
+	SQLiteMmap    string
+	LogLevel      string
+	LogFormat     string
+	ReadPoolSize  int
+	MaxUploadSize int64
+	Version       string
+	Commit        string
+	BuildDate     string
+	ShutdownTTL   time.Duration
+	Maintenance   time.Duration
+}
+
+func Load() (Config, error) {
+	cfg := Config{
+		Domain:        env("DOMAIN", "localhost"),
+		FilesDomain:   env("FILES_DOMAIN", ""),
+		InstanceName:  env("INSTANCE_NAME", "glchat"),
+		ListenAddr:    env("LISTEN_ADDR", DefaultListenAddr),
+		DataDir:       env("DATA_DIR", DefaultDataDir),
+		WebRoot:       env("WEB_ROOT", "/app/web"),
+		DatabasePath:  env("DATABASE_PATH", ""),
+		SQLiteCache:   env("SQLITE_CACHE_SIZE", "-8000"),
+		SQLiteMmap:    env("SQLITE_MMAP_SIZE", "134217728"),
+		LogLevel:      strings.ToLower(env("LOG_LEVEL", DefaultLogLevel)),
+		LogFormat:     strings.ToLower(env("LOG_FORMAT", "json")),
+		ReadPoolSize:  envInt("SQLITE_READ_POOL", 4),
+		MaxUploadSize: envInt64("MAX_UPLOAD_SIZE", 26214400),
+		Version:       env("APP_VERSION", "dev"),
+		Commit:        env("APP_COMMIT", "none"),
+		BuildDate:     env("APP_BUILD_DATE", "unknown"),
+		ShutdownTTL:   time.Duration(envInt("SHUTDOWN_TIMEOUT_SECONDS", 20)) * time.Second,
+		Maintenance:   time.Duration(envInt("DB_MAINTENANCE_INTERVAL_SECONDS", 21600)) * time.Second,
+	}
+	if cfg.FilesDomain == "" {
+		cfg.FilesDomain = "files." + cfg.Domain
+	}
+	if cfg.DatabasePath == "" {
+		cfg.DatabasePath = cfg.DataDir + "/db/glchat.db"
+	}
+	if cfg.ReadPoolSize < 1 {
+		return Config{}, fmt.Errorf("SQLITE_READ_POOL must be >= 1, got %d", cfg.ReadPoolSize)
+	}
+	if _, err := parseLogLevel(cfg.LogLevel); err != nil {
+		return Config{}, err
+	}
+	if cfg.LogFormat != "json" && cfg.LogFormat != "text" {
+		return Config{}, fmt.Errorf("LOG_FORMAT must be json or text, got %q", cfg.LogFormat)
+	}
+	return cfg, nil
+}
+
+func (c Config) BaseURL() string  { return "https://" + c.Domain }
+func (c Config) FilesURL() string { return "https://" + c.FilesDomain }
+
+func (c Config) LogLevelNumeric() int {
+	level, err := parseLogLevel(c.LogLevel)
+	if err != nil {
+		return 0
+	}
+	return level
+}
+
+func parseLogLevel(level string) (int, error) {
+	switch level {
+	case "debug":
+		return -4, nil
+	case "info":
+		return 0, nil
+	case "warn", "warning":
+		return 4, nil
+	case "error":
+		return 8, nil
+	default:
+		return 0, fmt.Errorf("unknown LOG_LEVEL %q", level)
+	}
+}
+
+func env(key, fallback string) string {
+	if v, ok := os.LookupEnv(key); ok && v != "" {
+		return v
+	}
+	return fallback
+}
+
+func envInt(key string, fallback int) int {
+	v, ok := os.LookupEnv(key)
+	if !ok || v == "" {
+		return fallback
+	}
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return fallback
+	}
+	return n
+}
+
+func envInt64(key string, fallback int64) int64 {
+	v, ok := os.LookupEnv(key)
+	if !ok || v == "" {
+		return fallback
+	}
+	n, err := strconv.ParseInt(v, 10, 64)
+	if err != nil {
+		return fallback
+	}
+	return n
+}