lint: social app fails due existing unused buildApiBaseFallback warning

Running `pnpm --filter social lint` reports a pre-existing warning:
`apps/social/src/App.tsx:116:10 'buildApiBaseFallback' is defined but never used` and lint fails because warnings are denied (`--max-warnings=0`).

This blocks clean lint in a single workspace and is unrelated to issue #300. Please remove the unused binding or rename with `_` prefix.
