fix(tools): preserve host PATH in Windows terminal snapshots - #71433

What does this PR do?

On Windows, build the LocalEnvironment snapshot with non-login Git Bash instead of bash -l.

Git for Windows' /etc/profile can replace the native parent PATH. Desktop and collaboration hosts commonly inject a bundled CLI directory into that parent environment before launching an ACP agent. The login shell discarded that directory before Hermes captured its terminal snapshot, so a CLI that existed and was present in the ACP process environment became command not found inside the terminal tool.

Configured shell init files are already prepended explicitly. This change keeps that behavior while limiting the non-login snapshot to Windows; POSIX retains the existing login-shell path.

Real integration proof

Reproduced on Windows 10 with:

• Buzz PR fix(signal): evict oldest sent timestamp instead of arbitrary one #2773 frozen at 0922869abe9f170879276588f3c4c51c292e230f
• installed hermes-acp.exe 0.19.0 launched directly
• one worker
• openai-codex:gpt-5.6-sol
• a Buzz-bundled CLI directory injected into the ACP process PATH

Before the change, native and non-login Git Bash could resolve buzz, while the login snapshot could not. After the change, a fresh process against current Hermes main returned:

/c/.../buzz-pr2773-pilot/build/target/release/buzz
BUZZ_CLI_OK

The full ACP turn then published a visible, attributed Buzz thread reply with the exact requested token.

The separate Git Bash startup-probe hang encountered in the same proof is already covered by #69083 and is intentionally not duplicated here.

Tests

• New Windows/POSIX shell-mode contract: 2 passed
• ruff check tools/environments/local.py tests/tools/test_local_env_windows_msys.py: passed
• Full Windows/MSYS file, baseline: 4 failed, 36 passed
• Full Windows/MSYS file, patched: 4 failed, 38 passed

The four failures are unchanged Windows-host baseline assumptions in existing tests; this patch introduced no new failures.

Type of change

• Bug fix
• Tests

Scope

• No configuration or new environment variables
• No provider/model changes
• No POSIX shell behavior change
• No third-party integration added to Hermes core