Landing: add I Ching epigraph and emphasize transforms / nature / destiny - #25

Root the landing tagline in the oldest recorded articulation of what
Be Framework is actually about: 乾道變化、各正性命 — from the Tuan
commentary on Qián (乾), the first hexagram of the I Ching (circa
4th Century BC).

Why this line, and why the landing page

  乾道變化   — As the Way transforms
  各正性命   — each thing settles into its nature and destiny

The two halves of the line mirror the two halves of Be Framework.

* 變化 (transformation) is metamorphosis. Be Framework's core loop —
  Input → Being → Final — is not a call stack, not a chain of
  responsibilities, not a pipeline of handlers. It is a sequence of
  transformations where a value becomes its next form. The same word
  the I Ching uses for cosmological change is the word we use for
  what a #[Be] attribute declares.

* 各正性命 (each settles into its nature and destiny) is the
  "Being-Oriented" half. 性 (nature) is what a thing *is* —
  intrinsic, non-behavioral. 命 (destiny / mandate) is what it was
  called to become. In a framework where final objects are immutable
  and every step is declared by what a value *will be*, not what a
  method *does*, 正性命 is not metaphor — it is the type signature.

Together the two halves name the same motion from opposite sides:
transformation happening everywhere, and each individual arriving
at what it was always going to be. That is the sentence a
Being-Oriented framework has been waiting to quote.

Translation choices

"settles into" rather than "is set right" or "fulfills". The
original 正 carries both the active sense (to rectify, to align)
and the intransitive sense (to come into alignment). English has
no single verb for "reach the position that was already yours,"
but "settles into" is closest — and it matches the experience of
reading a Be Framework pipeline, where nothing is forced into
place; each stage just arrives at what it had to be.

"nature and destiny" preserves both 性 and 命. Dropping either
collapses the pair that makes Be Framework legible: without 性
there is no Being, without 命 there is no Becoming.

Visual choices

* The Chinese is rendered invisibly via sr-only rather than
  displayed. The source matters — it should be searchable, indexed,
  and available to screen readers — but the landing page is for
  newcomers, not scholars of classical Chinese. The epigraph works
  the way a cornerstone works: load-bearing, rarely looked at.

* transforms / nature / destiny are bolded. These are the three
  words the tagline shares with the I Ching line, and they are the
  three words a reader of the manual will encounter again on every
  chapter. The bolding is not decoration; it is an index into the
  rest of the documentation.

* white-space: nowrap keeps the sentence unbroken. 乾道變化、
  各正性命 is a single breath in the original; the English should
  be too.

* The call to action shrinks from "Learn more »" to "be »".
  "Learn" is something you do to a topic from the outside. "be"
  is what the framework is named after, and the verb the next
  page will ask you to think in.

The previous inline white-space: nowrap applied universally and
caused horizontal overflow on narrow viewports, where the 71-char
English sentence cannot fit on one line at 1.8rem. Move the rule
into a media query (min-width: 1200px) scoped to .hero-tagline so
small screens wrap normally and nowrap kicks in only when the
viewport is actually wide enough to hold the single-breath line
the epigraph is modeled on.