v0.8.31 — fix install crash on read-only installs

Fixed

• mcptoon install no longer writes into the installed package (issue #35).
  Generated handler files were written to <package>/handlers/ — a path that is
  writable only when mcptoon is installed into the user's own tree. On a Nix store
  path (the reporter's case: PermissionError on
  site-packages/mcptoon/handlers), a system-wide pip install, a distro package
  or a container image the directory is read-only, so every mcptoon install
  crashed before recording the server. Handlers now live under the user's state
  dir (<state>/handlers, overridable with MCPTOON_HANDLERS_DIR), which is
  always writable and is cleaned up by mcptoon uninstall like the rest of
  mcptoon's state. The reporter's exact failure mode is pinned by a regression
  test that makes the package's handlers path raise PermissionError and
  asserts install still succeeds.