feat(docs): theme 2.0.0, the lighter blue accent, and a light/dark logo pair - #8

…go pair

Three things the landing surfaced when di joined it as the fifth panel
(btravstack/btravstack.github.io#43). Closes #6. Closes #7.

**The accent.** `--accent` was `#2A62B8`, the logo's deep blue. The landing
paints each package name in the raw accent against a `#100F12` card, and that
hex measures 3.22 there — the other four packages sit at 5.00–7.25. It is now
`#3E7FD4`, the logo's *lighter* blue: 4.72 on the dark card, 7.10 as darkened
text on white. The original reasoning is untouched and still holds — blue is
plumbing, and the hex is one the mark itself already paints (barrel rim,
plunger, needle hub), so chrome and artwork stay one color.

**The logo pair.** di shipped only `logo.svg`, and it was the one package
without a `logo-{light,dark}` pair. Three of its values read against the canvas
rather than against the artwork, so on a light background the near-white barrel
washed out and the mark read as a floating beet with a blue cap. `logo-dark` is
the existing file unchanged; `logo-light` inverts exactly those three — barrel
`#EAF2FB`→`#2A2730`, plunger `#2A62B8`→`#3E7FD4`, needle `#9FB2C8`→`#5A6675`.
The ticks stay at 50% opacity: 1.89 against the dark barrel versus 1.81 against
the light one, so they read equally faint either way. The hero and the nav logo
now take the pair; `logo.svg` stays the favicon and the JSON-LD mark.

**The theme.** Catalog moves 1.7.0 → 2.0.0, which is where `--pkg-di` lives.
The major is the removal of `--pkg-demesne` / `--pkg-start`; neither is
referenced here, so nothing breaks. pnpm recorded the new version as a pinned
`minimumReleaseAgeExclude` entry — replaced with the unversioned name and the
rationale comment the other repos use, so the next release needs no entry.

Docs build clean: `--accent: #3E7FD4` in the emitted CSS, no `2a62b8` left, all
five `--pkg-*` tokens present and both retired ones gone, and both logo variants
verified in both themes.

`pnpm format --check` failed CI on this file. oxfmt normalises CSS hex values
to lowercase, which is why every sibling site's `--accent` is lowercase and why
this file's own `#2a62b8` was before it changed. The comment's hex follows, so
the file does not mix cases with its own declaration.

Note this is the opposite of the markdown convention: prose in changesets and
`design.md` writes hexes uppercase. Each file type is internally consistent.

Root cause of the miss: the shared pre-commit hook in @btravstack/lefthook
globs `*.{ts,tsx,js,jsx,json,yaml,yml,md}`, which has no `css`, so this file was
never formatted locally — the hook reported three files (config.ts, index.md,
pnpm-workspace.yaml) and skipped this one. CI runs `oxfmt .` over everything.