Fix Neovim debug layout and reserve the window key prefix

[jiminu]

Toggling the file explorer during debugging could progressively widen the DAP sidebar. Preserve the current sidebar width and tray height across explorer changes, including buffered toggles and manual sizing. Close the explorer when a session initializes so it does not remain between debug panels and source; users can reopen it with Space e.

Move resize-mode entry from Space w to Space w r, leaving Space w available as a window-command prefix. Update documentation and runtime fixtures, and add an isolated Go runner for layout checks against approved plugin checkouts.

Also close the Git-decoration test process when its probe finishes, preventing its one-minute deadline from expiring during subsequent debugger E2E phases.

Validation:

• Local bash scripts/check.sh passed with pinned local Neovim plugins and TMPDIR=/private/tmp.
• After rebasing onto the documentation update, the DAP layout, DAP configuration, and editor configuration tests passed again.
• The Git-decoration probe and all three focused Neovim configuration/layout tests passed after the cleanup fix.