docs: mark all epic0 stories as completed

Update status of all epic0 stories (0.1-0.5) from Pending to Completed:
- 0.1: Project Initialization - Directory structure and Go module setup
- 0.2: Configuration Management System - Viper-based config implemented
- 0.3: Structured Logging System - Zap logger with middleware implemented
- 0.4: CI/CD Pipeline - GitHub Actions workflow with tests and linting
- 0.5: DI and Bootstrap - FX-based DI container with lifecycle management

All stories have been implemented with tests and are working.

docs/content/stories/epic0/0.4-cicd-pipeline.md

@@ -4,7 +4,7 @@
 - **Story ID**: 0.4
 - **Title**: CI/CD Pipeline and Development Tooling
 - **Epic**: 0 - Project Setup & Foundation
-- **Status**: Pending
+- **Status**: Completed
 - **Priority**: High
 - **Estimated Time**: 3-4 hours
 - **Dependencies**: 0.1