bug: Windows shell emulation paths are wrong

[ourchitectureio]

Plan for Windows POSIX shells path fixing

• Map current path-setting flow for proto activate: ExecWorkflow collects paths, reset_paths merges existing PATH via envx::paths, and print_activation_exports writes _PROTO_ACTIVATED_PATH plus shell-specific PATH via shell.format_path_set (crates/cli/src/commands/activate.rs, crates/cli/src/workflows/exec_workflow.rs). Confirm JSON path output (ActivateResult.path) uses reset_and_join_paths.
• Detect emulated POSIX shells on Windows (Git Bash/MSYS2/Cygwin) without touching real Linux/macOS or Windows CMD/PowerShell: gate logic on cfg!(windows) plus env hints like MSYSTEM, MINGW, MSYS, OSTYPE=msys|cygwin, and target shell types Bash/Zsh/Fish/Murex/Elvish.
• Add a Windows-only helper to translate host paths to emulated POSIX form (C:\Users\Alice → /c/Users/Alice, handle UNC \server\share → /unc/server/share, ignore already-posix strings). Keep it no-op outside the gated scenario.
• Apply the helper where proto activate emits paths for POSIX shells on Windows: convert workflow.paths and inherited PATH entries before _PROTO_ACTIVATED_PATH and format_path_set, and convert JSON ActivateResult.path when producing --json output for these shells. Leave command execution (apply_to_command) and non-emulated shells untouched.
• Tests: add unit tests for the converter covering drive-letter, UNC, trailing slashes, already-posix, and relative paths. Add a CLI-level test (Windows-only or using injected PATH strings) ensuring proto activate bash --export emits /c/... style entries while preserving ordering and leaving PowerShell/CMD outputs unchanged. Keep existing Unix snapshots intact.
• Docs/notes: mention the emulated-shell path normalization in relevant docs or changelog entry, and note explicitly that Linux/macOS behavior and native Windows shells are unaffected.