feat: Additive merge of webui branch with PyQt GUI support

- Add abogen/pyqt/ package with full PyQt6 desktop GUI
- Restore PyQt GUI files (gui.py, book_handler.py, queue_manager_gui.py, voice_formula_gui.py, conversion.py)
- Add new shared modules from webui: book_parser.py, subtitle_utils.py, spacy_utils.py
- Add Linux libraries (libxcb-cursor) for Qt platform plugin support
- Add new epub parsing tests from webui branch
- Update pyproject.toml with dual entry points:
  - abogen: PyQt6 desktop GUI
  - abogen-web: Flask Web UI
- Add PyQt6 to dependencies
- Re-export PyQt classes from root modules for backwards compatibility
- Merge CHANGELOG.md entries (1.2.0-1.2.5 from webui)
- Update README.md with dual interface documentation

Implements #26 - shared core with separate UI folders

pyproject.toml

@@ -34,7 +34,8 @@ dependencies = [
     "numpy>=1.24.0",
     "gpustat>=1.1.1",
     "num2words>=0.5.13",
-    "httpx>=0.27.0"
+    "httpx>=0.27.0",
+    "PyQt6>=6.5.0"
 ]
 
 classifiers = [
@@ -62,11 +63,12 @@ allow-direct-references = true
 
 
 [project.gui-scripts]
-abogen = "abogen.webui.app:main"
+abogen = "abogen.pyqt.main:main"
 
 [project.scripts]
 abogen-cli = "abogen.webui.app:main"
 abogen-web = "abogen.webui.app:main"
+abogen-pyqt = "abogen.pyqt.main:main"
 
 [tool.hatch.build.targets.sdist]
 exclude = [