Add “Enable Instructions” command to toggle instruction files

[fmachadopiriz]

Description

Add a new command named “Enable Instructions” that lets users enable/disable instruction files in the workspace.

Requirements

Find all files matching *instructions.md.
Enabled files keep the original *instructions.md name.
Disabled files are renamed to *instructions.md.bak.
When the command runs, show a command‑palette popup listing the files with checkboxes to enable/disable.
Initial checkbox state reflects the current filename (enabled if ends with instructions.md, disabled if ends with instructions.md.bak).

Acceptance criteria

Checking “enable” renames *instructions.md.bak → *instructions.md.
Checking “disable” renames *instructions.md → *instructions.md.bak.
Supports multiple files in one run.
Show a confirmation message after applying changes.