Add read-only Debug API support and update documentation

- Introduced a local read-only Debug API accessible at `http://127.0.0.1:17821` for diagnostics and agent interactions.
- Updated CLI commands to include `gpu-rent debug` for launching the Debug API.
- Enhanced documentation to reflect the new Debug API features and usage.
- Modified configuration to include `DEBUG_LOCAL_PORT` for easier customization.
- Added tests to ensure Debug API links are correctly generated in access card outputs.

env.example

@@ -43,6 +43,8 @@ SWARMUI_LOCAL_PORT=17801
 # WORKLOAD=llm          # llm-only (no SwarmUI); requires LLM_RUNTIME=ollama
 LLM_RUNTIME=none
 OLLAMA_LOCAL_PORT=17811
+# Localhost read-only Debug API (up/tunnel/debug) — agent: /openapi.json /snapshot
+DEBUG_LOCAL_PORT=17821
 # OLLAMA_MODELS_MANIFEST=
 # Pin Ollama (несecреты; удобнее в gpu-rent.vars):
 # OLLAMA_VERSION=0.6.5