feat: add agent module with Nginx service commands and routes

- Introduced a new agent module with commands for managing Nginx configurations.
- Implemented `NginxService` for handling reload, validation, and configuration writing.
- Added routes for status, validation, and configuration writing using Axum.
- Created necessary command files: `reload.rs`, `run.rs`, `validate.rs`, `write_config.rs`.
- Updated `Cargo.toml` and `Cargo.lock` to include new dependencies.
- Added `.gitignore` for the agent module.
- Updated `justfile` to include OpenAPI generation for the agent.

justfile

@@ -48,6 +48,11 @@ generate-openapi:
   # Generate API client for frontend
   cd apps/frontend && \
   pnpm generate:openapi
+  # Generate OpenAPI spec for agent
+  cd apps/agent && \
+  cargo run -- --generate-openapi --openapi-output ./openapi.yaml
+  # TODO: Generate API client for agent in api
+
 
 generate-all: generate-entity generate-openapi