fix(node): make init, node.toml editing and CLI output work on Windows

Found by running the daemon on Windows for the first time:

- `meshbay-node init` wrote `unlock_file = "C:\Users\..."`, and
  attach_group / add_root write `path = "C:\..."` — a raw Windows path in a
  TOML basic string is a parse error (`\U`, `\a`, ... are escape sequences),
  so the config would not load. All now write `Path(...).as_posix()`;
  pathlib reads the forward-slash form fine on Windows.
- any `print()` carrying a `->` arrow or em dash (the CLI help and messages
  are full of them) raised UnicodeEncodeError on a cp1252 console and took
  the command down. New `platform.force_utf8_stdio()` reconfigures
  stdout/stderr to UTF-8, called at the top of `main()`.

Verified on Windows: init writes parseable LF node.toml, the keystore
Argon2-decrypts, the loopback control API binds 127.0.0.1, and
`_update_node_toml` reads a CRLF file and rewrites it LF-only with its
standalone comments intact. Two regression tests added in test_ops.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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