Flag help prints words nobody wrote, for the same reason the errors did #127

#121 fixed the error messages that came out of the renderer with a word nobody wrote. The flag help has the same problem, from the same cause, and it is worse there, because a help line is where someone looks up what to type.

fang title-cases the first word of a flag's usage string the same way it does an error message. Forty-two help lines in this repo lose something to it:

ccrawl columnar count --engine   Auto|Duckdb|Native|Print (auto)
ccrawl columnar count --subset   Warc|Crawldiagnostics|Robotstxt (warc)
ccrawl fetch --order             Input|File: emit in the order given or the order on disk (file)
ccrawl fetch --file              Warc file path (relative to data.commoncrawl.org)
ccrawl parse --type              Warc-Type filter (response|request|metadata|...)
ccrawl parse --mime              Http MIME filter (substring)
ccrawl index build --input       Jsonl file of documents to index, or - for stdin
ccrawl index build --urls        Comma-Separated page URLs to fetch and index
ccrawl rank top --table          Url of a gzipped rank table
ccrawl host get --graph          Web-Graph release ID (default: latest)
ccrawl urls publish --repo       Huggingface dataset repo (org/name)
ccrawl urls publish --workers    Download-And-Convert workers (0 picks a default from CPU count)
ccrawl domains recount --workers Footer-Read workers (0 picks a default from CPU count)
ccrawl markdown refetch --rate   Per-Host request rate limit (req/s, 0 = unlimited)

The first two are the ones that actually mislead. --engine and --subset print a list of the values they take, and after the renderer every value in the list is spelled with a capital that the flag does not accept. The rest print a word that is not the word: Warc, Http, Jsonl, Url, Huggingface.

Same rule as #121, so the fix is the same: no help line starts with a word that title-casing damages. Reword them to lead with a plain lowercase word.

Two more come from any-cli rather than from here, --fields printing "Comma-Separated columns to show" and --timeout printing "Per-Request timeout". They need an upstream change and are out of scope for this issue.

Done when

• no flag in the tree prints a first word that was not written that way
• --engine and --subset print the values they accept
• a test fails on a new one, covering both ways a flag is declared here, the pflag call and the kit help tag
• the two any-cli flags are written down as upstream