feat: Add Content Generation Engine v2 with quality scoring

Major improvements to AI content generation:

## New Components (app/services/ai/)
- PromptLibrary: YAML-based prompt templates with inheritance
- ContextEngine: Anti-repetition and best performers tracking
- ContentGeneratorV2: Enhanced generation with dynamic parameters
- PlatformAdapter: Platform-specific content adaptation
- ContentValidator: AI-powered quality scoring (0-100)

## Prompt Library (app/prompts/)
- 3 personalities: default, educational, promotional
- 5 templates: tip_tech, product_post, service_post, thread, response
- 4 platform configs: x, threads, instagram, facebook
- Few-shot examples by category: ia, productividad, seguridad

## Database Changes
- New table: content_memory (tracks generated content)
- New columns in posts: quality_score, score_breakdown, generation_attempts

## New API Endpoints (/api/v2/generate/)
- POST /generate - Generation with quality check
- POST /generate/batch - Batch generation
- POST /quality/evaluate - Evaluate content quality
- GET /templates, /personalities, /platforms - List configs

## Celery Tasks
- update_engagement_scores (every 6h)
- cleanup_old_memory (monthly)
- refresh_best_posts_yaml (weekly)

## Tests
- Comprehensive tests for all AI engine components

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

app/models/post.py

@@ -102,6 +102,11 @@ class Post(Base):
     recycled_from_id = Column(Integer, ForeignKey("posts.id"), nullable=True)
     recycle_count = Column(Integer, default=0)  # Times this post has been recycled
 
+    # AI Generation Quality
+    quality_score = Column(Integer, nullable=True, index=True)  # 0-100 score from validator
+    score_breakdown = Column(JSON, nullable=True)  # Detailed scoring breakdown
+    generation_attempts = Column(Integer, default=1)  # Times regenerated before acceptance
+
     # Timestamps
     created_at = Column(DateTime, default=datetime.utcnow)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
@@ -136,7 +141,10 @@ class Post(Base):
             "ab_test_id": self.ab_test_id,
             "is_recyclable": self.is_recyclable,
             "recycled_from_id": self.recycled_from_id,
-            "recycle_count": self.recycle_count
+            "recycle_count": self.recycle_count,
+            "quality_score": self.quality_score,
+            "score_breakdown": self.score_breakdown,
+            "generation_attempts": self.generation_attempts
         }
 
     def get_content_for_platform(self, platform: str) -> str: