Add a force flag to bypass confirmation prompts; enable performance-level specification for the similar subcommand.

[venyowong]

First of all, thank you for open-sourcing this great project. neatcli fits my current needs very well, but I would like to integrate it into my project, and there are two areas that could be improved:

1. Add a force flag, because I want the program to run silently without user confirmation. Of course, I will inform users of the risks in advance when they use neatcli.

2. Since I will be using neatcli on ARM development boards, the default image hashing algorithm is a bit too heavy for the board. Therefore, I would like the similar command to support specifying a performance level.

Based on the above two points, I have modified some of the code to achieve these goals.

venyowong@bogon neatcli % ./target/release/neatcli similar -h                                             
Find visually similar images using perceptual hashing

Usage: neatcli similar [OPTIONS] [PATH]

Arguments:
  [PATH]  Target directory to scan [default: .]

Options:
  -t, --threshold <THRESHOLD>  Similarity threshold (0-256, lower = more strict, default: 10) [default: 10]
      --delete                 Delete similar images (keeps the first in each group)
  -n, --dry-run                Preview changes without executing
  -e, --execute                Actually execute the changes
      --force                  Clean without confirm
      --level <LEVEL>          Performance vs accuracy trade-off [default: balanced] [possible values: fast, balanced, high]
      --trash                  Move similar images to trash instead of permanent deletion
  -v, --verbose                Enable verbose output
  -q, --quiet                  Suppress all output except errors
  -h, --help                   Print help
  -V, --version                Print version