v0.3: PySide2 mini-UI panel + installer

- New: hermes_bridge_panel.py — PySide2 floating panel with:
  - Port configuration (spinner)
  - Open/Close toggle with green/red status
  - Auto-detected hostname
  - One-click copy prompt: 'Hey Hermes, I have Houdini on [host] port [N]'
  - Persists port setting across sessions
- New: install.py — auto-detects houdini dir, copies panel + shelf
- New: hermes_bridge.shelf — shelf tool integration
- Updated: README with panel usage instructions

houdini/shelf/hermes_bridge.shelf

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<shelfDocument>
+  <tools>
+    <tool name="hermes_bridge" label="Hermes Bridge" icon="MISC_python">
+      <script scriptType="python"><![CDATA[
+import sys
+sys.path.insert(0, hou.getenv("HHB_PATH") or hou.homeHoudiniDirectory() + "/scripts/python")
+exec(open(hou.homeHoudiniDirectory() + "/scripts/python/hermes_bridge_panel.py").read())
+hermes_bridge_panel.show()
+]]></script>
+    </tool>
+  </tools>
+</shelfDocument>