Add install.sh for Devcontainer dotfiles integration

[Copilot]

Devcontainers require an install.sh script at the repository root to automatically install dotfiles when the container is created.

Changes

• install.sh: Symlinks dotfiles to $HOME on execution
  • Links .zshrc, .profile, .vim to home directory
  • Links each .config/ subdirectory individually (alacritty, clangd, git, nvim, tmux)
  • Backs up existing files with .backup suffix before overwriting
  • Idempotent - safe to run multiple times
  • Uses ASCII output for cross-terminal compatibility

Usage

# Devcontainer runs this automatically, or invoke manually:
./install.sh

# Output:
Installing dotfiles from /path/to/dotfiles
Installing shell configuration files...
  [OK] Linked /home/user/.zshrc -> /path/to/dotfiles/.zshrc
  [OK] Linked /home/user/.profile -> /path/to/dotfiles/.profile
...
[SUCCESS] Dotfiles installation complete!

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create install.sh</issue_title>
<issue_description>That would make it possible for the Devcontainers to install dotfiles seamlessly.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create install.sh #20

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