refactor(watcher): extract auth synthesis logic into separate synthesizer package

internal/watcher/synthesizer/interface.go

@@ -0,0 +1,16 @@
+// Package synthesizer provides auth synthesis strategies for the watcher package.
+// It implements the Strategy pattern to support multiple auth sources:
+// - ConfigSynthesizer: generates Auth entries from config API keys
+// - FileSynthesizer: generates Auth entries from OAuth JSON files
+package synthesizer
+
+import (
+	coreauth "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/auth"
+)
+
+// AuthSynthesizer defines the interface for generating Auth entries from various sources.
+type AuthSynthesizer interface {
+	// Synthesize generates Auth entries from the given context.
+	// Returns a slice of Auth pointers and any error encountered.
+	Synthesize(ctx *SynthesisContext) ([]*coreauth.Auth, error)
+}