fix: make -h/--human-readable actually apply

[VXNCXNX]

Closes #880.

The problem

-h / --human-readable is parsed and then never used:

$ grep -rn human_readable src/
src/app.rs:61:    human_readable: bool,

One hit, the declaration. Nothing reads it. So the flag has no effect at all:

$ lsd -l --size bytes -h
5000                 <- raw bytes, -h ignored

The fix

Make -h and --size override each other, so the later flag wins:

lsd -l --size bytes -h            ->  4.9 KB     (was 5000)
lsd -l -h --size bytes            ->  5000       (--size wins, as it should)
lsd -l --size bytes -h --size short -> 4.9M      (last of three wins)

This uses clap's overrides_with, which the repo already relies on for all/almost_all in the same file, and args_override_self = true is already set on the struct, so it's the existing idiom rather than manual index comparison.

--classic still takes precedence over both, unchanged. Config-file size: still works and the CLI still beats it:

config size: bytes                 ->  5000
config size: bytes  +  CLI -h      ->  4.9 KB

One change that needs a sentence

human_readable had to become pub so flags/size.rs can read it, which left help: () as the struct's only private field, and that newly trips clippy's manual_non_exhaustive. I made help pub too, matching every other field.

I checked whether this is a public API concern: it isn't. lsd has no lib target (only [[bin]] in Cargo.toml) and mod app; is private in main.rs, so Cli is unreachable from outside the crate. The alternative clippy suggests, #[non_exhaustive], would be wrong here since clap needs the field.

Tests

Four tests added to flags/size.rs's existing test module, covering both orderings, --classic precedence, and the config interaction.

cargo build:         clean
cargo test:          395 passed (unit), 44 passed (integration)
cargo fmt --check:   clean
cargo clippy --all-targets: no new warnings in the changed files

One integration test, test_date_custom_format_supports_nanos_with_length, fails in my environment on a locale decimal separator. It fails identically on a clean checkout, so it's unrelated to this change.

---

TODO

• Use cargo fmt (cargo fmt --check clean)
• Add necessary tests (four in flags/size.rs)
• Update README (if applicable) (not applicable: the README already documents -h/--human-readable; this makes the documented behaviour true rather than changing it)
• Update config sample file in doc/samples (if applicable) (not applicable: no config key is added or changed, the size: key is unchanged)
• Update icon sample file in doc/samples (if applicable) (not applicable: no icon change)
• Update color sample file in doc/samples (if applicable) (not applicable: no color change)
• Update man page at lsd/doc/lsd.md (if applicable) (not applicable: the man page already documents -h/--human-readable)

Disclosure: written with AI assistance (Claude Code). I reproduced the issue, ran the change and the verification myself.