Rework the landing top into a left-anchored hero row and match the
navbar branding to it.
- `index.rst` + new `tractor_hero.html`: an inline-svg hero
(`[logo] distributed structured concurrency`) with a full-width
sub-tagline, plus a single screen-reader-only `<h1>` ("tractor")
so the section headings become proper `<h2>` (was 4x `<h1>`), and
the intro prose reflowed into 3 bullets,
- `conf.py`: a `logo.text` ("tractor") beside the navbar wireframe,
polars-style,
- `custom.css`: the hero-row layout (logo + tagline + sub-line,
single row on desktop / stack on mobile), the navbar brand styled
like the centered nav tabs with `display:inline-block` to kill
the parent link's propagated hover-underline, and smaller landing
section headings w/ their `tl;dr` margin-note pulled level.
The hero linework stays `fill: currentColor` so the whole thing
flips with the light/dark toggle.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi