docs(kit): describe what a token does, not which look uses it

[Bccorb]

Summary

Four comments in index.css explained a token by naming the looks that set it:

• display-stretch was "the whole distance between Blueprint's condensed
  capitals and Cinematic's expanded ones"
• data-cell was "a kit decision: Console is tight, Cinematic is loose"
• rule was "hairline in most kits, heavy in Editorial, double in Almanac"
• auto-grid was "two columns in Cinematic and four in Blueprint"

None of those names exist in this repository. They belong to one consumer's set of
themes, so the stylesheet was documenting somebody else's product rather than the
lever it actually ships, and a project scaffolded from here reads these comments
with no idea what any of it refers to.

Follows #57, which removed the last literal reference
of that kind from the README. This is the same problem in a milder form.

What changed

Comments only. No token, value, selector or class is touched, so the built CSS is
byte for byte what it was. Each comment now says what a theme can do with the
token: one download covering condensed through expanded, a readout wanting tight
rows against a showy theme wanting loose ones, a hairline a theme may make heavy
or double into a masthead rule, an airy theme landing on two columns where a dense
one lands on four.

Release impact

No changeset. Comments do not reach a scaffolded project's behaviour.

Checks

npm run validate and npm run format:check both pass. The two template copies
are synced from shared/react-app as usual, which is why three files change for
one edit.