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/install.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+"""
+Install Hermes Bridge into Houdini.
+
+Copies the Python panel to ~/houdini21.0/scripts/python/
+and the shelf tool to ~/houdini21.0/toolbar/
+
+Usage: python install.py [--houdini-dir ~/houdini21.0]
+"""
+import os
+import sys
+import shutil
+import argparse
+
+FILES = {
+    "hermes_bridge_panel.py": "scripts/python/",
+    "hermes_bridge.shelf": "toolbar/",
+}
+
+
+def get_houdini_dir():
+    """Auto-detect Houdini prefs directory."""
+    home = os.path.expanduser("~")
+    for d in sorted(os.listdir(home), reverse=True):
+        if d.startswith("houdini") and os.path.isdir(os.path.join(home, d)):
+            return os.path.join(home, d)
+    return os.path.join(home, "houdini21.0")
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Install Hermes Bridge into Houdini")
+    parser.add_argument(
+        "--houdini-dir",
+        default=get_houdini_dir(),
+        help=f"Houdini preferences directory (default: {get_houdini_dir()})",
+    )
+    args = parser.parse_args()
+
+    src_dir = os.path.dirname(os.path.abspath(__file__))
+
+    for filename, subdir in FILES.items():
+        src = os.path.join(src_dir, filename)
+        dst_dir = os.path.join(os.path.expanduser(args.houdini_dir), subdir)
+        dst = os.path.join(dst_dir, filename)
+
+        if not os.path.exists(src):
+            print(f"  SKIP {filename} — source not found")
+            continue
+
+        os.makedirs(dst_dir, exist_ok=True)
+        shutil.copy2(src, dst)
+        print(f"  COPY {filename} -> {dst}")
+
+    print(f"\nInstalled to {args.houdini_dir}")
+    print("Restart Houdini — the shelf tool appears under 'Hermes Bridge'.")
+
+
+if __name__ == "__main__":
+    main()