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>

alembic/env.py

@@ -16,9 +16,13 @@ sys.path.insert(0, str(Path(__file__).parent.parent))
 
 from app.core.config import settings
 from app.core.database import Base
+# Import all models for autogenerate support
 from app.models import (
     User, Product, Service, TipTemplate,
-    Post, ContentCalendar, ImageTemplate, Interaction
+    Post, ContentCalendar, ImageTemplate, Interaction,
+    PostMetrics, AnalyticsReport, Lead, OdooSyncLog,
+    ABTest, ABTestVariant, RecycledPost, ThreadSeries, ThreadPost,
+    ContentMemory
 )
 
 # this is the Alembic Config object