Cut the landing page back to a landing page

[okcodes]

The first version of the page restated the documentation. Refusals with their
reasoning, the version state machine, eleven exit codes, the safety guarantees,
the argument for one vump.toml per repository — all lifted from README.md
and DESIGN.md. That is two copies of the same claims to keep true, and a
first-time visitor reading a specification before learning what the tool is.

This cuts it back to a landing page: what does it do, does it handle my files,
how do I start. Everything deeper is a link to the repository, which stays the
only place the behaviour is written down.

What went

The defect essay, the prompting rule in long form, the transition table, the
"Refused, deliberately" cards, the exit-code grid, the safety guarantees, the
lock-file and .NET explanations, and the numbered sections — numbering reads as
a document, and this is not one.

Monorepos survive as a single block, because "does it handle my repo" is a
question someone evaluating the tool actually has.

What is there now

Four sections. Three cards saying what it does, a file picker showing the one
line that changes in your own file, a workflow snippet with the failure it
catches, and a three-step start. The page is 4,400px instead of 10,000, and the
headline commits to a plain claim — one command — instead of a promise about
tags that means nothing before you know what the tool is.

Two bugs fixed along the way

The social card was rendering from corrupted fonts. The three woff2 files
were decompressed with Promise.all, a change made earlier to satisfy
no-await-in-loop. The decompressor is a single emscripten module with one
heap, so overlapping calls corrupt each other's output — two of the three fonts
came back as invalid TrueType, differently on each run. The renderer falls back
silently rather than reporting a font it cannot parse, so the only symptom was
an image that rendered every line in whichever face survived. Sequential
decompression, with the rule disabled on those lines and the reason above them.

Layout items sized to their scrolling content. A grid or flex item defaults
to min-width: auto and will not shrink below its content, so an item holding a
terminal or snippet dragged the document wider than a phone screen. Fixed once
per item in the first branch and back immediately with the monorepo block, so it
is now the default for children of grid and flex containers, written with
:where() so anything that wants a minimum still overrides it.

pnpm

Both lockfiles were in the tree after pnpm-lock.yaml landed on main.
package-lock.json is gone, Prettier no longer checks the lockfile, and the
commands and the deployment workflow in website/README.md are pnpm.

Still not deployed

Unchanged from the last branch: the base path is baked into every asset URL at
build time and the domain is not settled. website/README.md has the table of
what to set and the workflow ready to paste.