Restore GraphQL schema merge for Relay query text

relay-compiler requires a single schema file: a directory is rejected
and schemaExtensions marks fields as client-only, so it emitted
text: null and the console posted query: null, getting a 400 on every
operation.

Restore the merge step (contrib/merge-graphql-schema.sh, the
RELAY_SCHEMAS make rules, and the gitignore entry) and point each
relay.config.json project back at the merged schema.graphql. The IDE
graphql-config removal and npm-script cleanup are unrelated and stay.

Signed-off-by: Émile Ré <emile@probo.com>

.gitignore

@@ -21,6 +21,7 @@ compose/keycloak/probo-realm.json
 # Generated files (codegen)
 __generated__/
 pkg/server/api/*/v1/types/types.go
+pkg/server/api/*/v1/schema.graphql
 cfg/dev_local.yaml
 cfg/dev.yaml
 .env