Update all dependencies and migrate to new Google genai SDK

- Update all Go dependencies to latest versions
- Migrate from github.com/google/generative-ai-go/genai to google.golang.org/genai
- Fix google.go to use the new SDK API (NewPartFromText, NewContentFromParts, etc.)
- Update schema package imports to use the new genai package
- Add CLAUDE.md with README maintenance guideline

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

schema/array.go

@@ -4,8 +4,8 @@ import (
 	"errors"
 	"reflect"
 
-	"github.com/google/generative-ai-go/genai"
 	"github.com/openai/openai-go"
+	"google.golang.org/genai"
 )
 
 type array struct {