Initial scaffold with per-nameserver DNS monitoring model

Full project structure following upaas conventions: uber/fx DI, go-chi
routing, slog logging, Viper config. State persisted as JSON file with
per-nameserver record tracking for inconsistency detection. Stub
implementations for resolver, portcheck, tlscheck, and watcher.

internal/logger/logger.go

@@ -0,0 +1,83 @@
+// Package logger provides structured logging with slog.
+package logger
+
+import (
+	"log/slog"
+	"os"
+
+	"go.uber.org/fx"
+
+	"sneak.berlin/go/dnswatcher/internal/globals"
+)
+
+// Params contains dependencies for Logger.
+type Params struct {
+	fx.In
+
+	Globals *globals.Globals
+}
+
+// Logger wraps slog.Logger with level control.
+type Logger struct {
+	log    *slog.Logger
+	level  *slog.LevelVar
+	params Params
+}
+
+// New creates a new Logger with TTY detection for output format.
+func New(_ fx.Lifecycle, params Params) (*Logger, error) {
+	loggerInstance := &Logger{
+		level:  new(slog.LevelVar),
+		params: params,
+	}
+	loggerInstance.level.Set(slog.LevelInfo)
+
+	isTTY := detectTTY()
+
+	var handler slog.Handler
+
+	if isTTY {
+		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+			Level:     loggerInstance.level,
+			AddSource: true,
+		})
+	} else {
+		handler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+			Level:     loggerInstance.level,
+			AddSource: true,
+		})
+	}
+
+	loggerInstance.log = slog.New(handler)
+
+	return loggerInstance, nil
+}
+
+func detectTTY() bool {
+	fileInfo, err := os.Stdout.Stat()
+	if err != nil {
+		return false
+	}
+
+	return (fileInfo.Mode() & os.ModeCharDevice) != 0
+}
+
+// Get returns the underlying slog.Logger.
+func (l *Logger) Get() *slog.Logger {
+	return l.log
+}
+
+// EnableDebugLogging sets the log level to debug.
+func (l *Logger) EnableDebugLogging() {
+	l.level.Set(slog.LevelDebug)
+	l.log.Debug("debug logging enabled", "debug", true)
+}
+
+// Identify logs application startup information.
+func (l *Logger) Identify() {
+	l.log.Info("starting",
+		"appname", l.params.Globals.Appname,
+		"version", l.params.Globals.Version,
+		"buildarch", l.params.Globals.Buildarch,
+	)
+}