fix(web): rename xAI display labels to SpaceXAI

[chrarnoldus]

Summary

• rename xAI user-facing provider labels to SpaceXAI
• keep provider IDs, model IDs, environment variables, and protocol values unchanged
• update the network compliance diagram label

Validation

• pnpm --filter web run lint
• pnpm --filter web run typecheck
• pnpm --filter web exec jest src/lib/notifications/byok-provider-cache.test.ts --runInBand
• pnpm exec oxfmt on changed TypeScript files
• git diff --check