chore: let renovate resolve the lockfile with legacy peer deps (#17765)

Renovate's artifact step fails with ERESOLVE on every npm PR, so it
opens them with `package.json` updated and `package-lock.json` left
behind, drifting the lockfile until `npm ci` breaks.

The conflict is the root pinning graphql@17.0.2 against
@apollo/cache-control-types, which requires 14.x || 15.x || 16.x.
CI already works around this by installing with
`npm install --legacy-peer-deps`; this gives Renovate the same setting
so its lockfile step resolves the same way CI does.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

renovate.json

@@ -1,6 +1,7 @@
 {
   "extends": ["config:base", ":dependencyDashboard"],
   "labels": ["dependencies"],
+  "npmrc": "legacy-peer-deps=true",
   "packageRules": [
     {
       "matchDepTypes": ["devDependencies"],