docs(vercel): lead with the four-step deploy, and fix the install e2e

The page predated the Deploy Button. It told the reader to import their
own repository, set a build command of `community migrate && forum-web
build` — without `--at-root`, so the artefact lands where Vercel does not
read it — and to bring their own managed Postgres, Redis, mail provider
and domain. All four now arrive with the deploy.

It opens with the route: press the button, connect the four products,
generate two secrets, deploy, open /install. Everything that is not a step
moved behind it, split into what decides whether the route suits you at
all and what to come back to when the platform behaves unlike a server.
The manual route is kept whole under its own heading, with the build
command corrected and the requirements table that used to be at the top.

The two anchors other documents link to are preserved verbatim.

The install e2e started from a genuinely empty database and relied on the
installer to migrate it, so it failed on its first step rather than
reaching the validation error it was written to test. The fixture had
conflated applying the schema with inserting fixture rows under one flag;
they are separate now, and the install database carries the schema with no
rows — the state a board is genuinely in when someone opens /install. A
genuinely empty one would fail that step, and correctly so.

Author: claude

docs/README.md

@@ -17,7 +17,7 @@ This directory is the source for [meith.dev/docs](https://www.meith.dev/docs). C
 
 - [Quickstart](./quickstart.md) — deploy with Coolify on your own server.
 - [Deploying by hand](./self-hosting.md) — use Docker Compose with a reverse proxy you operate.
-- [Running on Vercel](./vercel.md) — deploy onto functions instead of a server: the driver set, the cron tick, build-time migrations, and how to leave.
+- [Running on Vercel](./vercel.md) — deploy onto functions instead of a server: the four-step Deploy Button route, then the quirks worth knowing — the cron tick, build-time migrations, and how to leave.
 - [Demo mode](./demo-mode.md) — run a public board that resets itself.
 
 ## Administer a community

docs/development.md

@@ -632,8 +632,15 @@ coverage floor when runtime behavior is introduced.
 
 `pnpm test:e2e` starts everything it needs: a PGlite serving the Postgres
 wire protocol, a built server running the standalone output against it, and
-a second empty database and server for `/install`. There is nothing to
-install and nothing to leave running.
+a second database and server for `/install`. There is nothing to install
+and nothing to leave running.
+
+That second database carries the schema and no rows, which is the state a
+board is actually in when someone opens `/install`: migrations run before
+the board serves anything — from the container entrypoint, or from the
+deploy build command — and the installer checks the schema rather than
+applying it. A genuinely empty database would fail its first step, and
+correctly so.
 
 **Most specs run with JavaScript disabled** — 33 of the 48 spec files. That
 is the point rather than a flourish: this board's claim is that a native