fix(mcphub-nvim): disable make_vars to prevent codecompanion crash

[syltharion]

Closes #1777

Sets make_vars = false in the mcphub codecompanion extension config. When mcphub loads before codecompanion is fully initialized, make_vars = true triggers variable registration that crashes with 'bad argument #1 to pairs (table expected, got nil)'.

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

• Proper usage of opts table rather than setting things up with the config function.

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).

[Uzaaft]

This seems like a hack.
Instead you should make one load the other if defined or something... Disabling isn't the way.