Document the database, the seed and signing in locally

[davidtaing]

The getting-started instructions were written when the stack came up empty and nothing read it. They still told a contributor to boot Supabase and then stopped — no mention of what a reset seeds, no way to sign in, and two paragraphs asserting that no page queries the database.

What this adds

The seed. What supabase/seed.sql loads and why two different kinds of thing share one file: the 24 real credentials, canonical in supabase/seed/credential-catalogue.json, and the invented population #110 added. So a reset leaves a directory with something in it and stable handles at /p/seed0001 … /p/seed0008. And the part that bites — the loader is additive, so an edit to it reaches a stack through pnpm db:reset and by no other route.

Signing in. The three seeded addresses and what each one is for, and Mailpit as where the link arrives. Worth its own section because "magic link only" reads like a missing step until you know there is no password to be given: there is nothing to type and nothing to commit.

A Tests section, which the README did not have. It listed pnpm test:e2e under Scripts and neither Vitest project.

The point that prompted this: pnpm test:db uses the same database pnpm dev does. There is no second stack, and it is not a read-only suite — it writes fixtures, signs accounts up and deletes them, and revokes a column grant to prove the trigger refuses the write without it. A clean run puts all of that back; an interrupted one leaves a stray profile in your directory or a privilege your next query is missing. So resetting often is the workflow rather than a recovery step, and the section says so.

Two failures that send you to the wrong file go with it:

• the suite reports skipped rather than failed when the stack is not answering, so read the exit code and not the summary line;
• Kong keeps routing to the auth container's pre-reset address, which 502s every sign-up — and breaks sign-in from pnpm dev too, so the Signing in section points at the same one-line fix.

Corrections carried along

"The placeholder home page", and "Nothing in the app queries any of it yet" / "What has not happened yet is a read" — all three were false once the above went in. The migration enumeration was already stale at six of eight, and is now a pointer to supabase/migrations/ and AGENTS.md rather than a count that rots on the next one.

Note

AGENTS.md still says seven migrations and carries neither the shared-database nor the Kong note. Left alone deliberately — this is the setup document, and AGENTS.md is a separate edit that would collide with the branch it is currently being changed on.

Docs only, so no Schema run.