fix: drop netifaces (unbuildable on runner), harden build install

The packaged exe crashed with ModuleNotFoundError: No module named 'PySide6'.
Root cause: `pip install -e .` aborted because netifaces has no wheel for the
build's Python and needs MSVC to compile from source, so NO dependencies were
installed — and the workflow didn't catch it (native-command failures don't
trip $ErrorActionPreference, and the next pip command succeeded).

- Replace netifaces with a dependency-free socket-based LAN IP detection in the
  GUI; remove netifaces from pyproject and all PyInstaller specs.
- Make pip failures fatal (check $LASTEXITCODE) and add a "Verify runtime
  imports" step that fails the build before bundling if any dep is missing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -39,7 +39,6 @@ A cross-platform macro management application with desktop and web interfaces. C
 - PyAutoGUI (Keyboard automation)
 - Pillow (Image processing)
 - pystray (System tray)
-- netifaces (Network detection)
 - qrcode (QR code generation)
 - aiohttp (Relay server client)