Add CI/CD linting workflow for code quality checks

[stoicneko]

Summary

This PR introduces a comprehensive GitHub Actions workflow to automatically lint and validate code across multiple languages and formats used in the project.

Key Changes

• Fish syntax validation: Automatically checks all .fish files for syntax errors using the Fish shell compiler
• Lua code formatting: Validates Lua files in the nvim/ directory using StyLua to ensure consistent code style
• YAML linting: Lints YAML configuration files (specifically install.conf.yaml) using yamllint with relaxed rules
• Dotbot installation test: Verifies that the dotbot installation script runs successfully with all submodules

Implementation Details

• The workflow runs on every push to main and on all pull requests targeting main
• Each linting task runs independently on ubuntu-latest to allow parallel execution
• The Fish syntax check iterates through all .fish files and fails the job if any syntax errors are detected
• StyLua is installed via the official GitHub Action for consistency and ease of updates
• The dotbot test includes recursive submodule checkout to ensure the full installation environment is tested

https://claude.ai/code/session_01Ds2c5H1AZig4ZMXFsfU46D