feat(memory): add memory consolidation task and switch source_episode_ids to JSON

- Added `memory_consolidation` to the task list and updated `__all__` in test files.
- Updated `source_episode_ids` in `Fact` model to use JSON for cross-database compatibility.
- Revised related database migrations to use JSONB instead of ARRAY.
- Adjusted test concurrency in Makefile for improved test performance.

backend/Makefile

@@ -80,7 +80,7 @@ test:
 
 test-cov:
 	@echo "🧪 Running tests with coverage..."
-	@IS_TEST=True PYTHONPATH=. uv run pytest --cov=app --cov-report=term-missing --cov-report=html -n 16
+	@IS_TEST=True PYTHONPATH=. uv run pytest --cov=app --cov-report=term-missing --cov-report=html -n 20
 	@echo "📊 Coverage report generated in htmlcov/index.html"
 
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