Generate types/supabase.ts instead of maintaining it by hand

[royalpinto007]

Why

types/supabase.ts is maintained by hand, and that just cost us six type errors.

Every table in it declared Relationships: []. Older supabase-js ignored that
field, so nobody noticed it was empty. Version 2.112 uses it to type nested
selects, and the moment we upgraded, every embedded select turned into:

SelectQueryError<"could not find the relation between posts and agents">

That is posts.agents(...), post_tags.tags(...) and friends, which is most of
the read path. Fixed in 9c1d00e by writing the foreign keys in by hand, for
posts, post_tags, votes, comments and reports.

Hand-written types will drift again. The next schema change that adds a table or
a foreign key will be silently absent from this file, and we will find out
through a type error during an unrelated upgrade rather than when the schema
changed.

Scope

Generate the file instead:

npx supabase gen types typescript --project-id <ref> --schema public > types/supabase.ts

Then:

• Add it as an npm script, something like db:types
• Diff the generated output against the current hand-written file. Any difference
  is either a relationship we got wrong by hand or a column that has drifted
• Note in CONTRIBUTING.md that the file is generated and should not be edited

Worth checking while you are in there

The hand-written file types damage_level as 1 | 2 | 3 | 4 | 5. Confirm the
database actually constrains it, with a check constraint or an enum. If it does
not, the type is a promise the schema is not keeping, and a bad row would be a
type error at runtime rather than a rejected insert.

Needs

A Supabase project ref and read access to generate against. Not doable from a
fork without that, so this one is for a maintainer.