Bash completion script

[iconoclasthero]

Add bash completion for Timeshift

This adds a bash completion script for Timeshift. It includes:

• Completion for all the main options (--list, --create, --restore, etc.)
• Snapshot name completion for --snapshot using timeshift --list
• Safe shell quoting for snapshot names (even though Timeshift snapshot names don't contain spaces, this keeps it robust)
• Tag completion for --tags

The script is silent if timeshift --list fails or if there are no snapshots, so there are no side effects.

This addresses the feature request FR #502.

It’s placed in a standard bash-completion style and should work for both user and system-wide installations.

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Testing Instructions

1. Copy or link the completion script to your local bash-completion directory:

# system-wide (requires root)
sudo cp timeshift-completion.bash /etc/bash_completion.d/

# OR user-only
mkdir -p ~/.local/share/bash-completion/completions
sudo cp timeshift-completion.bash ~/.local/share/bash-completion/completions/timeshift

2. Reload bash (or source the script directly for quick testing):

# Reload current shell
source ~/.bashrc

# OR source the script directly
source ./timeshift-completion.bash

3. Test completion:

# Should complete main options
timeshift --<TAB>

# Should complete snapshot names from `timeshift --list`
timeshift --snapshot <TAB>

# Should complete tags for `--tags`
timeshift --tags <TAB>

4. Verify that completion is safe and no side effects occur if no snapshots exist.