log: Use the SimpleHandler by default

Instead of defaulting to slog.defaultHandler, we now use the
SimpleHandler which we were already using when SetOutput was called.

This produces log messages without the date, so instead of:

    2025/08/27 22:15:32 DEBUG Verbosity: 2

It logs:

    22:15:32 DEBUG Verbosity: 2

Author: adombeck

log/log.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"log/slog"
 	"maps"
+	"os"
 	"sync"
 	"sync/atomic"
 )
@@ -20,7 +21,7 @@ type (
 )
 
 var logLevelMu = sync.RWMutex{}
-var logLevel slog.Level
+var logLevel = NoticeLevel
 
 var hasCustomOutput atomic.Pointer[io.Writer]
 
@@ -64,6 +65,10 @@ var defaultHandlers = map[Level]Handler{
 var handlers = maps.Clone(defaultHandlers)
 var handlersMu = sync.RWMutex{}
 
+func init() {
+	SetOutput(os.Stderr)
+}
+
 // GetLevel gets the standard logger level.
 func GetLevel() Level {
 	logLevelMu.RLock()