Prebuilt executables, CLI flags and real CI (v0.2.0)

[Mattbusel]

• Code moves to token_visualizer.py (importable, pipx-installable); "Token Visualizer.py" stays as a shim.
• --model/--no-color/--version, piped input no longer blocks on the tokenizer menu, special tokens counted, lazy transformers import, UTF-8/ANSI on Windows, pause-before-close when double-clicked.
• pytest suite + CI that fails on failure (Linux + Windows).
• Tag-triggered release workflow: PyInstaller single-file executables for Windows, macOS arm64/Intel, Linux with tiktoken encodings bundled (smoke-tested offline behind a dead proxy) and SHA256SUMS.txt.