fix: preserve spaced Windows shim command lines
Windows agent setup fails when the resolved npx.cmd path contains spaces: cmd.exe /s /c strips the executable quotes and tries to run the first path component. Preserve a fully quoted command line through the shared resolver and its setup, skill-install, and upgrade callers.
The wrapper disables delayed expansion, preserves trailing backslashes and empty arguments, and retains the shell-metacharacter rejection with CR/LF also rejected. No command or flag changes.
Validation: typecheck, build, and all 107 local test files pass (2259 tests; one Windows-only test skipped on macOS). The new Windows regression executes a real .cmd shim under a spaced path and checks literal argv, including empty arguments, trailing backslashes, parentheses, and exclamation marks. Windows CI passed all 11 tests in this regression file; its full suite passed 2213 tests with 47 platform-specific skips. Linux CI also passed.
Independent self-review and mutation checks completed before push. Cubic reported no issues across all 8 files. No release is included.