feat: convert to pip package

- Restructure repo into hermes_identity_plugin/ Python package
- Add pyproject.toml with setuptools build config
- Register identity entry point under hermes_agent.plugins
- Include plugin.yaml, .json, .yaml as package data
- Update README with pip install instructions and project layout

hermes_identity_plugin/plugin.yaml

@@ -0,0 +1,11 @@
+name: identity
+version: 1.0.0
+description: >
+  Identity resolution plugin for Hermes. Maps platform-specific user IDs
+  (Discord snowflake, Telegram UID, terminal) and kanban boards to stable
+  Honcho peer names. Config file at /opt/data/identity-config.json for
+  persistence across container rebuilds.
+author: "@gortium"
+hooks:
+  - pre_gateway_dispatch
+  - on_session_start