Add PR validation workflow

[trippwill]

Summary

• install nightly Neovim in GitHub Actions for PRs
• install plenary.nvim for tests
• install Rust and use vimcats to verify docs
• update README to require nvim 0.11+

Testing

• bash ./test.sh (fails: E492: Not an editor command: PlenaryBustedDirectory)

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https://chatgpt.com/codex/tasks/task_e_68442e84a3f0832e9e093800fe601227

[Copilot]

Pull Request Overview

Adds a GitHub Actions workflow to validate pull requests by installing dependencies and running docs checks and tests.

• Introduce a pr.yml workflow that sets up Neovim nightly, Rust toolchain, and caching for Cargo and Plenary.nvim
• Add a docs verification step using vimcats
• Update README to bump required Neovim version to 0.11+

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
doc/swapdiff.nvim.txt	Simplified list-item wording but removed list markers
README.md	Updated Neovim requirement from 0.9 to 0.11
.github/workflows/pr.yml	New PR validation workflow with setup, caching, docs check, and tests

Comments suppressed due to low confidence (2)

doc/swapdiff.nvim.txt:432

• The leading '-' list marker was removed, which may break vimdoc list formatting. Consider restoring the '-' prefix for consistent list items.

PrintLogSink writes log messages to the Neovim message area using `print()`.

README.md:15

• The list bullet ('- ') was dropped before **Requirements:**, causing inconsistent Markdown list formatting. Re-add - **Requirements:**.

**Requirements:** Neovim 0.11+