[cmpadden]

Summary

• Remove the vendored nvim-image-paste implementation, README, and tests now maintained in https://github.com/cmpadden/nvim-image-paste.
• Prefer the local ~/src/nvim-image-paste development checkout when available, otherwise install the external plugin with vim.pack.
• Pin the external plugin revision in nvim-pack-lock.json.
• Preserve the existing setup call, insert-mode Ctrl-V mapping, and :ImagePaste command.

Validation

• make lint passed, using a temporary uvx environment for ShellCheck.
• make format passed after staging the removed files.
• Headless integration checks passed for both the local-checkout loader and a fresh GitHub fallback install in isolated XDG directories, including plugin setup, command registration, and mappings.
• External plugin suite: 15 paste tests and 9 health tests passed, including macOS tests using a private pasteboard.
• Audited the staged additions for sensitive information and unrelated changes.

Scope

The Neovim light-theme prototype, other plugin-lock changes, line-number preference, and LSP keymap changes remain local and are not part of this PR.