feat(cms): Sentry server instrumentation + withSentryConfig + R38 PII test

Adds apps/cms/instrumentation.ts (server-only — Payload admin client DSN
is out-of-scope per spec §8). Wraps the Payload-wrapped next config with
withSentryConfig. Adds the R38 PII scrubber test. Required adding
@repo/core-shared as a direct dep of cms (was only transitive before).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cms/package.json

@@ -16,6 +16,8 @@
     "@payloadcms/richtext-lexical": "^3.14.0",
     "@payloadcms/ui": "^3.14.0",
     "@repo/core-cms": "workspace:*",
+    "@repo/core-shared": "workspace:*",
+    "@sentry/nextjs": "^10.51.0",
     "next": "^15.3.0",
     "payload": "^3.14.0",
     "react": "^19.0.0",