feat(core-realtime): scaffold realtime optional core

Generator-emitted scaffold (pnpm turbo gen core-package realtime) plus
the story-00-precedent coverage repairs (coverage provider devDep,
symbols.ts exclude + tested allowlist mirror) and three minimal tests
covering generator-emitted realtime code the template suite misses.
Squash of 31d85e0 + review-fix cf11b38.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

apps/web-next/next.config.mjs

@@ -11,6 +11,7 @@ const nextConfig = {
     "@repo/core-consent",
     "@repo/core-dsr",
     "@repo/core-events",
+    "@repo/core-realtime",
     "@repo/core-shared",
     "@repo/core-trpc",
     "@repo/core-ui",