feat: add shell completion support for bash, zsh, and fish
- Add core/cli/completion.go with dynamic completion script generation
- Add core/cli/completion_test.go with unit tests
- Modify cmd/local-ai/main.go to support completion command
- Modify core/cli/cli.go to add Completion subcommand
- Add docs/content/features/shell-completion.md with installation instructions
The completion scripts are generated dynamically from the Kong CLI model,
so they automatically include all commands, subcommands, and flags.
Co-authored-by: localai-bot <localai-bot@noreply.github.com>
