Remove unused files: old UI, build scripts, fonts, test files

Remove old widget-based Python UI (replaced by QML), unused build
scripts, NL/variable/webfont variants, old shaders, PNG icons
(replaced by SVGs), and standalone test files. Add build.bat and
build.spec for the bootstrapper build system.

build.bat

@@ -0,0 +1,31 @@
+@echo off
+echo ============================================
+echo   Building WhisperVoice Portable EXE
+echo ============================================
+echo.
+
+if not exist venv (
+    echo ERROR: venv not found. Run run_source.bat first.
+    pause
+    exit /b 1
+)
+
+call venv\Scripts\activate
+
+echo Running PyInstaller (single-file bootstrapper)...
+pyinstaller build.spec --clean --noconfirm
+
+if %ERRORLEVEL% NEQ 0 (
+    echo.
+    echo BUILD FAILED! Check errors above.
+    pause
+    exit /b 1
+)
+
+echo.
+echo Build complete!
+echo.
+echo Output: dist\WhisperVoice.exe
+echo.
+echo This single exe will download all dependencies on first run.
+pause