Fix Tool exec failing on Windows paths with parentheses

When the appose base envs dir contains parentheses (e.g. Fiji(1)/envs),
cmd.exe /c misinterprets the parentheses as shell metacharacters, causing
pixi.exe invocation to fail and is_installed() to return False.

Fix by invoking absolute-path executables directly via subprocess instead
of wrapping them in cmd.exe /c -- native .exe files don't need shell
wrapping, and bypassing cmd.exe avoids all metacharacter issues.

Also improve the "not installed" error message to distinguish between
"executable not found" and "executable exists but failed to run", and
include the expected path in both cases.

As per apposed/appose-java@bc86914

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ctrueden

src/appose/tool/__init__.py

@@ -167,7 +167,17 @@ def exec(self, *args: str, cwd: Path | None = None) -> None:
             RuntimeError: If the tool has not been installed.
         """
         if not self.is_installed():
-            raise RuntimeError(f"{self.name} is not installed")
+            command_path = Path(self.command)
+            if command_path.is_file():
+                raise RuntimeError(
+                    f'{self.name} is installed at "{self.command}"'
+                    " but could not be run -- the path may contain characters"
+                    " that are special to the shell (e.g. parentheses on Windows)"
+                )
+            raise RuntimeError(
+                f"{self.name} is not installed"
+                f' (expected executable at "{self.command}")'
+            )
 
         self._do_exec(cwd=cwd, silent=False, include_flags=True, args=args)
 
@@ -278,8 +288,16 @@ def _do_exec(
         self._captured_output.clear()
         self._captured_error.clear()
 
-        # Build command
-        cmd = platform.base_command()
+        # Build command.
+        # On Windows, cmd.exe /c is needed for shell scripts and PATH resolution,
+        # but absolute paths to native executables must be invoked directly:
+        # cmd.exe treats parentheses and other characters as shell metacharacters,
+        # so a path like C:\Users\foo\Fiji(1)\bin\pixi.exe would be misinterpreted.
+        cmd = (
+            []
+            if platform.is_windows() and Path(self.command).is_absolute()
+            else platform.base_command()
+        )
         cmd.append(self.command)
         if include_flags:
             cmd.extend(self._flags)