[HARD] Implement Full Config-Driven MLOps Pipeline Runner

**Description:**
Create a pipeline orchestrator that runs stages based on YAML configuration.

**Requirements:**
- Commands:
  - `python pipeline.py --stage all`
  - `python pipeline.py --stage preprocess`
  - `python pipeline.py --stage train_lstm`
- Save logs → `logs/pipeline.log`.

**Acceptance Criteria:**
- Modular stage execution.
- Clear failure handling.