feat(nvim): load generated Noctalia colors

[CollieIsCute]

Summary

• add the base16 plugin expected by Noctalia's generated lua/matugen.lua
• load the generated module when it exists
• keep the generated palette outside chezmoi ownership

This is the same minimal loader that Noctalia's official Neovim apply hook creates at runtime, now managed declaratively on every platform.

Verification

• loaded the plugin spec with headless Neovim
• executed matugen.setup() against the current generated palette and asserted the resulting base16 color
• ran a targeted chezmoi dry-run
• git diff --check

References

• https://github.com/noctalia-dev/community-templates/blob/main/neovim/apply.sh
• https://github.com/noctalia-dev/community-templates/blob/main/neovim/matugen-template.lua
• https://github.com/RRethy/base16-nvim#readme