fix(backend): use JSON-array form of contains() for jsonb shared_with

PostgrestFilterBuilder's .contains(column, value) serializes a JS
array as PostgreSQL array literal '{a,b}', which is the right shape
for text[] columns but invalid input for jsonb. Two of three call
sites (projects.ts and access.ts) passed bare arrays, causing every
GET /projects request to return 500 with 'invalid input syntax for
type json' on vanilla Postgres+PostgREST. The third site
(tabular.ts:107) already uses JSON.stringify([...]) - this commit
makes the other two match.

Tested by tracing the generated PostgREST URL: bare array produces
'cs.{smoke@test.local}' (4xx), JSON.stringify produces
'cs.["smoke@test.local"]' (200).