Add configuration files and comprehensive project documentation

- Add .env.backup with full application configuration template
- Create RequestIDMiddleware for trace ID injection in logs
- Implement ARQ fallback pool for Redis unavailability
- Add Dead Letter Queue module for failed job handling
- Include project ROADMAP with audit and 27 applied corrections
- Add Grafana monitoring dashboard with 10 panels

.env.backup

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+# ============================================================
+# Imago — Configuration
+# Copier ce fichier en .env et remplir les valeurs
+# ============================================================
+
+# Application
+APP_NAME="Imago"
+APP_VERSION="1.0.0"
+DEBUG=true
+SECRET_KEY="changez-moi-en-production-avec-une-cle-aleatoire-longue"
+
+# AI — Configuration
+AI_ENABLED=true
+
+# AI — Provider (gemini/openrouter)
+AI_PROVIDER="openrouter"
+
+# Serveur
+HOST=0.0.0.0
+PORT=8000
+
+# Base de données
+# DATABASE_URL="sqlite+aiosqlite:///./data/imago.db"
+# Pour PostgreSQL (Docker):
+DATABASE_URL="postgresql+asyncpg://imago:imago@db:5432/imago"
+
+# Redis (ARQ Worker)
+REDIS_URL="redis://redis:6379/0"
+
+# Stockage des fichiers
+STORAGE_BACKEND="s3"
+UPLOAD_DIR="./data/uploads"
+THUMBNAILS_DIR="./data/thumbnails"
+MAX_UPLOAD_SIZE_MB=50
+
+# S3 / MinIO
+S3_BUCKET="imago"
+S3_REGION="us-east-1"
+S3_ENDPOINT_URL="http://minio:9000"
+S3_ENDPOINT_PUBLIC="http://localhost:9000"
+S3_ACCESS_KEY="minioadmin"
+S3_SECRET_KEY="minioadmin"
+S3_PREFIX="imago"
+
+# AI — Google Gemini
+GEMINI_API_KEY="AIzaSyATeU2LOAwcTjxYcTo9DTfq_B6U9Rakj2U"
+GEMINI_AI_MODEL="gemini-3.1-pro-preview"
+AI_MAX_TOKENS=1024
+
+# AI - Openrouter
+OPENROUTER_API_KEY="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"
+OPENROUTER_AI_MODEL="qwen/qwen2.5-vl-72b-instruct"
+
+
+# AI — Comportement
+AI_TAGS_MIN=5
+AI_TAGS_MAX=10
+AI_DESCRIPTION_LANGUAGE="français"
+AI_CACHE_DAYS=30
+
+# OCR
+OCR_ENABLED=true
+TESSERACT_CMD="/usr/bin/tesseract"
+OCR_LANGUAGES="fra+eng"
+
+# CORS
+CORS_ORIGINS=["http://localhost:3000","http://localhost:8080","http://localhost:5173"]
+
+# Rate Limiting (requêtes par minute)
+RATE_LIMIT_UPLOAD=10
+RATE_LIMIT_AI=20
+ADMIN_API_KEY=imago-admin-key