Simplify runtime providers

[RyanLee-Dev]

Summary

• remove local Docker sandbox provider and Docker socket requirements
• keep runtime surface to manual daemon and E2B-compatible cloud provider
• update Create Agent and Runtime UI to Cloud (E2B) / Local device, with default local daemon surfaced
• clean docs, install scripts, compose, CI, and OpenAPI around the new runtime model

Verification

• go test ./server/...
• pnpm --filter @parsar/web typecheck
• docker compose -f docker-compose.yml config --quiet
• git diff --check