fix: Fix YAML syntax errors and validator prompt formatting

- Fix YAML files with unquoted strings containing quotes
- Export singleton instances in ai/__init__.py
- Fix validator scoring prompt to use replace() instead of format()
  to avoid conflicts with JSON curly braces

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

app/services/ai/__init__.py

@@ -9,16 +9,23 @@ Este módulo contiene los componentes del motor de generación de contenido:
 - ContentValidator: Validación y scoring con IA
 """
 
-from app.services.ai.prompt_library import PromptLibrary
-from app.services.ai.context_engine import ContextEngine
-from app.services.ai.generator import ContentGeneratorV2
-from app.services.ai.platform_adapter import PlatformAdapter
-from app.services.ai.validator import ContentValidator
+from app.services.ai.prompt_library import PromptLibrary, prompt_library
+from app.services.ai.context_engine import ContextEngine, context_engine
+from app.services.ai.generator import ContentGeneratorV2, content_generator_v2
+from app.services.ai.platform_adapter import PlatformAdapter, platform_adapter
+from app.services.ai.validator import ContentValidator, content_validator
 
 __all__ = [
+    # Classes
     "PromptLibrary",
     "ContextEngine",
     "ContentGeneratorV2",
     "PlatformAdapter",
     "ContentValidator",
+    # Singleton instances
+    "prompt_library",
+    "context_engine",
+    "content_generator_v2",
+    "platform_adapter",
+    "content_validator",
 ]