docs: finalize documentation for Go migration

Updated README, architecture, and TODO to reflect full feature parity, system metrics, and registry integration.

README.md

@@ -102,7 +102,13 @@ Access the dashboard at `http://localhost:8080`.
 ### Default Credentials
 
 - **Username:** `admin`
-- **Password:** `admin` (You will be prompted to change this or should change it manually in the dashboard)
+- **Password:** `admin123` (You will be prompted to change this on first login)
+
+**Forgot Password?**
+You can reset the admin password to default by running:
+```bash
+./llm-proxy -reset-admin
+```
 
 ## API Usage