Convert to pip package

- Moved __init__.py and plugin.yaml into hermes_piper_plugin/ package directory
- Added pyproject.toml with build config and entry point registration
- Updated tests to reference new subdirectory paths
- Updated README with pip-based installation instructions

This converts the plugin from a flat layout (loaded via hermes plugins install)
to a proper pip package with the 'hermes_agent.plugins' entry point.

README.md

@@ -24,19 +24,24 @@ import is safe. The plugin also logs the effective default at session start.
 ## Installation
 
 ```bash
-# 1. Ensure piper-tts is installed
-pip install piper-tts
+# Install from the internal Hermes package registry
+pip install hermes-piper-plugin
 
-# 2. Install the plugin from the internal Hermes repo
-hermes plugins install ssh://git@code.lazyworkhorse.net:2222/Hermes/hermes-piper-plugin.git
-
-# 3. Restart gateways to load the plugin
+# Or install in editable mode for development
+git clone https://code.lazyworkhorse.net/gortium/hermes-piper-plugin.git
+cd hermes-piper-plugin
+pip install -e .
 ```
 
+> **Note:** The plugin used to be installed via `hermes plugins install` from the
+> old flat layout. It is now a proper pip package. The entry point
+> `hermes_agent.plugins` is registered automatically when you install the
+> package — Hermes discovers it on next startup.
+
 ## Testing
 
 ```bash
-cd /opt/data/projects/hermes-piper-plugin
+cd /path/to/hermes-piper-plugin
 pip install pytest pyyaml
 python -m pytest tests/ -v
 ```