refactor(watcher): split watcher.go into focused modules

- Create dispatcher.go for auth update queue management
- Create events.go for fsnotify event handling
- Create config_reload.go for hot-reload logic
- Create clients.go for client lifecycle management
- Simplify watcher.go to core coordinator (~150 lines)
- Maintain 100% API backward compatibility
- All tests passing with 72%+ coverage

internal/watcher/config_reload.go

@@ -0,0 +1,134 @@
+// config_reload.go implements debounced configuration hot reload.
+// It detects material changes and reloads clients when the config changes.
+package watcher
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"time"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/watcher/diff"
+	"gopkg.in/yaml.v3"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func (w *Watcher) stopConfigReloadTimer() {
+	w.configReloadMu.Lock()
+	if w.configReloadTimer != nil {
+		w.configReloadTimer.Stop()
+		w.configReloadTimer = nil
+	}
+	w.configReloadMu.Unlock()
+}
+
+func (w *Watcher) scheduleConfigReload() {
+	w.configReloadMu.Lock()
+	defer w.configReloadMu.Unlock()
+	if w.configReloadTimer != nil {
+		w.configReloadTimer.Stop()
+	}
+	w.configReloadTimer = time.AfterFunc(configReloadDebounce, func() {
+		w.configReloadMu.Lock()
+		w.configReloadTimer = nil
+		w.configReloadMu.Unlock()
+		w.reloadConfigIfChanged()
+	})
+}
+
+func (w *Watcher) reloadConfigIfChanged() {
+	data, err := os.ReadFile(w.configPath)
+	if err != nil {
+		log.Errorf("failed to read config file for hash check: %v", err)
+		return
+	}
+	if len(data) == 0 {
+		log.Debugf("ignoring empty config file write event")
+		return
+	}
+	sum := sha256.Sum256(data)
+	newHash := hex.EncodeToString(sum[:])
+
+	w.clientsMutex.RLock()
+	currentHash := w.lastConfigHash
+	w.clientsMutex.RUnlock()
+
+	if currentHash != "" && currentHash == newHash {
+		log.Debugf("config file content unchanged (hash match), skipping reload")
+		return
+	}
+	log.Infof("config file changed, reloading: %s", w.configPath)
+	if w.reloadConfig() {
+		finalHash := newHash
+		if updatedData, errRead := os.ReadFile(w.configPath); errRead == nil && len(updatedData) > 0 {
+			sumUpdated := sha256.Sum256(updatedData)
+			finalHash = hex.EncodeToString(sumUpdated[:])
+		} else if errRead != nil {
+			log.WithError(errRead).Debug("failed to compute updated config hash after reload")
+		}
+		w.clientsMutex.Lock()
+		w.lastConfigHash = finalHash
+		w.clientsMutex.Unlock()
+		w.persistConfigAsync()
+	}
+}
+
+func (w *Watcher) reloadConfig() bool {
+	log.Debug("=========================== CONFIG RELOAD ============================")
+	log.Debugf("starting config reload from: %s", w.configPath)
+
+	newConfig, errLoadConfig := config.LoadConfig(w.configPath)
+	if errLoadConfig != nil {
+		log.Errorf("failed to reload config: %v", errLoadConfig)
+		return false
+	}
+
+	if w.mirroredAuthDir != "" {
+		newConfig.AuthDir = w.mirroredAuthDir
+	} else {
+		if resolvedAuthDir, errResolveAuthDir := util.ResolveAuthDir(newConfig.AuthDir); errResolveAuthDir != nil {
+			log.Errorf("failed to resolve auth directory from config: %v", errResolveAuthDir)
+		} else {
+			newConfig.AuthDir = resolvedAuthDir
+		}
+	}
+
+	w.clientsMutex.Lock()
+	var oldConfig *config.Config
+	_ = yaml.Unmarshal(w.oldConfigYaml, &oldConfig)
+	w.oldConfigYaml, _ = yaml.Marshal(newConfig)
+	w.config = newConfig
+	w.clientsMutex.Unlock()
+
+	var affectedOAuthProviders []string
+	if oldConfig != nil {
+		_, affectedOAuthProviders = diff.DiffOAuthExcludedModelChanges(oldConfig.OAuthExcludedModels, newConfig.OAuthExcludedModels)
+	}
+
+	util.SetLogLevel(newConfig)
+	if oldConfig != nil && oldConfig.Debug != newConfig.Debug {
+		log.Debugf("log level updated - debug mode changed from %t to %t", oldConfig.Debug, newConfig.Debug)
+	}
+
+	if oldConfig != nil {
+		details := diff.BuildConfigChangeDetails(oldConfig, newConfig)
+		if len(details) > 0 {
+			log.Debugf("config changes detected:")
+			for _, d := range details {
+				log.Debugf("  %s", d)
+			}
+		} else {
+			log.Debugf("no material config field changes detected")
+		}
+	}
+
+	authDirChanged := oldConfig == nil || oldConfig.AuthDir != newConfig.AuthDir
+	forceAuthRefresh := oldConfig != nil && oldConfig.ForceModelPrefix != newConfig.ForceModelPrefix
+
+	log.Infof("config successfully reloaded, triggering client reload")
+	w.reloadClients(authDirChanged, affectedOAuthProviders, forceAuthRefresh)
+	return true
+}