Replace zerolog with log/slog from stdlib

- Rewrite logger package to use slog with LevelVar for dynamic levels
- Update all packages to use *slog.Logger instead of *zerolog.Logger
- Use TextHandler for TTY (dev), JSONHandler for production
- Add make check target (runs lint + test)
- Add make test target

internal/healthcheck/healthcheck.go

@@ -2,13 +2,13 @@ package healthcheck
 
 import (
 	"context"
+	"log/slog"
 	"time"
 
 	"git.eeqj.de/sneak/gohttpserver/internal/config"
 	"git.eeqj.de/sneak/gohttpserver/internal/database"
 	"git.eeqj.de/sneak/gohttpserver/internal/globals"
 	"git.eeqj.de/sneak/gohttpserver/internal/logger"
-	"github.com/rs/zerolog"
 	"go.uber.org/fx"
 )
 
@@ -22,7 +22,7 @@ type HealthcheckParams struct {
 
 type Healthcheck struct {
 	StartupTime time.Time
-	log         *zerolog.Logger
+	log         *slog.Logger
 	params      *HealthcheckParams
 }