test: make the suite run under Windows

Windows spells a path with backslashes, and three fixtures took the POSIX shape: a config value written into a TOML basic string read `C:\users\…` as an escape, tool arguments built with an f-string broke the same way, and a root was compared as `str(path)` against `/srv/skills`. Paths are encoded with `json.dumps` (whose escaping is valid TOML and valid JSON) and compared as `Path` objects, so the same root matches in either spelling.

`test_interrupt.py` delivers SIGINT with `os.kill(pid, SIGINT)`, which is `TerminateProcess` on Windows, and the router itself needs `add_signal_handler`: the module is skipped there.

`python scripts/wine_pdm.py ci` is green: ruff, basedpyright 0 errors, 1156 passed / 30 skipped.

tests/test_cli/test_grants_cmd.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 from typing import TYPE_CHECKING
 
 import pytest
@@ -147,7 +148,10 @@ async def test_config_allow_paths_installed(
 ) -> None:
     outside = (tmp_path.parent / "outside-config").resolve()
     outside.mkdir(exist_ok=True)
-    document = tomlkit.parse(f'[agent]\nallow_paths = {{ "{outside}" = "read", "/does/not/exist" = "read" }}\n')
+    # JSON string escaping is TOML escaping too, so a Windows path's backslashes
+    # survive instead of reading as an escape (``\u``).
+    key = json.dumps(str(outside))
+    document = tomlkit.parse(f'[agent]\nallow_paths = {{ {key} = "read", "/does/not/exist" = "read" }}\n')
     state, memory = await _new_state(tmp_path, document=document)
     try:
         assert state.instance_state.workspace.config_allow == {outside: AccessMode.READ}