Server now handles all parsing/routing/peering/lookup (T11-T14). Client
sends the trimmed username verbatim to /api/social/requests and surfaces
server errors via toast (added in T18-T20).
Note: FriendsPage.tsx and UserProfileModal.tsx will fail to compile
until T19 and T20 remove their now-dead try/catch blocks for the
deleted error classes. TypeScript catches it; pnpm dev will not start
until those tasks land.