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/__init__.py

@@ -19,6 +19,7 @@ from app.models.odoo_sync_log import OdooSyncLog
 from app.models.ab_test import ABTest, ABTestVariant
 from app.models.recycled_post import RecycledPost
 from app.models.thread_series import ThreadSeries, ThreadPost
+from app.models.content_memory import ContentMemory
 
 __all__ = [
     "Base",
@@ -38,5 +39,6 @@ __all__ = [
     "ABTestVariant",
     "RecycledPost",
     "ThreadSeries",
-    "ThreadPost"
+    "ThreadPost",
+    "ContentMemory"
 ]