Add comprehensive test suite for image processing and related services

- Implement tests for database generator to ensure proper session handling.
- Create tests for EXIF extraction and conversion functions.
- Add tests for image-related endpoints, ensuring proper data retrieval and isolation between clients.
- Develop tests for OCR functionality, including language detection and text extraction.
- Introduce tests for the image processing pipeline, covering success and failure scenarios.
- Validate rate limiting functionality and ensure independent counters for different clients.
- Implement scraper tests to verify HTML content fetching and error handling.
- Add unit tests for various services, including storage and filename generation.
- Establish worker entry point for ARQ to handle background image processing tasks.

Makefile

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+.PHONY: help install install-dev lint format test test-cov serve worker docker-up docker-down clean
+
+help: ## Affiche l'aide
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | \
+		awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-18s\033[0m %s\n", $$1, $$2}'
+
+# ── Installation ──────────────────────────────────────────────
+
+install: ## Installer les dépendances de production
+	pip install -r requirements.txt
+
+install-dev: ## Installer les dépendances de dev + pre-commit
+	pip install -r requirements-dev.txt
+	pre-commit install
+
+# ── Qualité du code ───────────────────────────────────────────
+
+lint: ## Linter le code (ruff check + mypy)
+	ruff check app/ tests/
+	mypy app/ --ignore-missing-imports
+
+format: ## Formater le code (ruff format)
+	ruff format app/ tests/
+	ruff check --fix app/ tests/
+
+# ── Tests ─────────────────────────────────────────────────────
+
+test: ## Lancer les tests
+	python -m pytest tests/ -v --tb=short
+
+test-cov: ## Lancer les tests avec couverture
+	python -m pytest tests/ -v --tb=short --cov=app --cov-report=term-missing --cov-report=html
+
+# ── Serveur ───────────────────────────────────────────────────
+
+serve: ## Démarrer le serveur de développement
+	uvicorn app.main:app --reload --host 0.0.0.0 --port 8000
+
+worker: ## Démarrer le worker ARQ
+	python worker.py
+
+# ── Docker ────────────────────────────────────────────────────
+
+docker-up: ## Démarrer tous les services Docker
+	docker-compose up -d --build
+
+docker-down: ## Arrêter tous les services Docker
+	docker-compose down -v
+
+# ── Nettoyage ─────────────────────────────────────────────────
+
+clean: ## Nettoyer les fichiers temporaires
+	find . -type d -name __pycache__ -exec rm -rf {} + 2>/dev/null || true
+	find . -type d -name .pytest_cache -exec rm -rf {} + 2>/dev/null || true
+	find . -type d -name .mypy_cache -exec rm -rf {} + 2>/dev/null || true
+	find . -type d -name htmlcov -exec rm -rf {} + 2>/dev/null || true
+	find . -name "*.pyc" -delete 2>/dev/null || true