feat: add comprehensive CLI with API client, session management, and data seeding

- Binary renamed from 'api' to 'xevion' with full CLI command structure
- Authentication: login/logout with session persistence to .xevion-session
- API commands: projects, tags, settings CRUD operations with JSON/table output
- Serve command: run production server with configurable listen addresses
- Seed command: moved from bin/ to CLI subcommand for database initialization
- HTTP client abstraction supporting both TCP and Unix socket connections

.gitignore

@@ -6,7 +6,8 @@ target/
 web/build/
 web/.svelte-kit/
 
+# CLI session file
+.xevion-session
 
 # Added by cargo
-
 /target