__init__(version) Export __version__ from __about__

why: gp_sphinx.config.make_linkcode_resolve() reads __version__ via
getattr(package_module, "__version__", ""), falling back to "" and
generating broken sphinx source-link URLs like blob/v/src/...
what:
- Add from .__about__ import __version__ to __init__.py
- Add __all__ = ["__version__"]

Author: tony

src/libtmux_mcp/__init__.py

@@ -2,6 +2,10 @@
 
 from __future__ import annotations
 
+from .__about__ import __version__
+
+__all__ = ["__version__"]
+
 
 def main() -> None:
     """Entry point for the libtmux MCP server."""