feat(BAT-005): add broker credential CLI command with persistence and tests

- Add CredentialService for managing broker credentials
- Implement credential CLI commands (create, list, get, update, delete)
- Add postgres repository support for credential operations
- Add comprehensive test coverage for credential CLI
- Update docs/batches/index.md and docs/srs/index.md with BAT-005
- Update docs/project-structure.md to reflect credential service

app/cli/main.py

@@ -13,6 +13,7 @@ from app.cli.commands.service_tokens import token_app
 from app.cli.commands.portfolio import portfolio_app
 from app.cli.commands.strategy import strategy_app
 from app.cli.commands.user import user_app
+from app.cli.commands.credential import credential_app
 from app.core.config import Settings, get_settings
 from app.repositories.factory import get_portfolio_repository_from_settings
 from app.repositories.portfolio_repository import PortfolioRepository
@@ -51,6 +52,7 @@ def create_app(
     app.add_typer(strategy_app, name="strategy")
     app.add_typer(user_app, name="user")
     app.add_typer(token_app, name="service-token")
+    app.add_typer(credential_app, name="credential")
     register_health_commands(app)
     return app