v0.3.0

• Add --shell / -s flag to explicitly set the shell format (bash, zsh)
• Add zsh history format support, including filterZsh and test samples filterLines now handles zsh EXTENDED_HISTORY.
• Modularize filterLines and related code into filter.zig
• Remove Completion enum; clean up internal API
• Remove fallback history file detection; require $HISTFILE to be set
• Parameterize tests and fuzz over ShellEnum for both bash and zsh coverage
• Add fuzz tests and shell value error tests for --shell
• Update man page, README, and completions for all new flags and behavior
• Remove outdated Limitations sections from README and man page
• Fix lazy analysis of parse_args.zig so its test blocks are included in zig build test