Prefer OpenClaw client talk session creation

[rogerchappel]

Summary

• Start realtime Talk with talk.client.create, matching the installed OpenClaw dashboard
• Preserve the existing talk.session.create gateway-relay fallback for older/current compatibility
• Cover both primary and fallback paths in the Gateway client realtime tests

Verification

• pnpm test -- src/lib/gateway-client-realtime.test.ts 'src/app/api/runtimes/[id]/talk/realtime/relay/route.test.ts'\n- pnpm typecheck\n- git diff --check\n- pre-push hook: pnpm typecheck && pnpm build\n\n## Notes\nThe local OpenClaw dashboard at 127.0.0.1:18789 uses talk.client.create before falling back to talk.session.create, so this brings CrewCMD closer to that working client path.