Fix Relay generating null query text for mutations

Relay v20 treats extend type in server schema as client extensions,
causing all mutation fields to have "text": null in generated artifacts.

Replace the cat-based schema concatenation with a merge script that
collects all extend type Mutation blocks and produces a single
type Mutation definition. The split graphql/ files remain the source
of truth for gqlgen; the merged schema.graphql is generated for Relay.

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

contrib/merge-graphql-schema.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+# Merge split GraphQL schema files into a single file for Relay.
+# Strips "type Mutation" and "extend type Mutation { ... }" blocks,
+# then appends a single "type Mutation { ... }" with all collected fields.
+#
+# Usage: merge-graphql-schema.sh <output> <graphql-dir>
+
+set -eu
+
+output="$1"
+graphql_dir="$2"
+base="$graphql_dir/base.graphql"
+
+mutation_fields=$(mktemp)
+schema_body=$(mktemp)
+trap 'rm -f "$mutation_fields" "$schema_body"' EXIT
+
+process_file() {
+    awk -v mf="$mutation_fields" '
+    /^type Mutation$/ { next }
+    /^(extend )?type Mutation \{/ { skip=1; depth=1; next }
+    skip {
+        if (/\{/) depth++
+        if (/\}/) { depth--; if (depth==0) { skip=0; next } }
+        if (skip) { print >> mf; next }
+    }
+    { print }
+    ' "$1"
+}
+
+{
+    process_file "$base"
+    for f in "$graphql_dir"/*.graphql; do
+        [ "$f" = "$base" ] && continue
+        process_file "$f"
+    done
+} > "$schema_body"
+
+{
+    cat "$schema_body"
+    printf '\ntype Mutation {\n'
+    cat "$mutation_fields"
+    printf '}\n'
+} > "$output"