Add WebUI terminal login

[GodBlf]

Summary

• add CubeAPI WebSocket terminal bridge backed by the existing EnvD process PTY API
• add xterm-based WebUI terminal panel on sandbox list/detail pages, including resize, fullscreen/font controls, reconnect messaging, and container selection when metadata is available
• expose terminal message models, docs, i18n resources, OpenAPI/schema updates, and backend/frontend tests

Related issue: #642

Validation

• cargo test --manifest-path CubeAPI/Cargo.toml
• cargo test terminal --manifest-path CubeAPI/Cargo.toml
• npm run test --prefix web
• npm run build --prefix web
• cargo fmt --manifest-path CubeAPI/Cargo.toml --check
• git diff --check
• remote CubeSandbox validation on 192.168.12.85: WebUI same-origin WebSocket connected through :12088, executed shell commands, verified ANSI bytes, resize, concurrent session isolation, unauthorized 401, and terminal.session open/close audit logs

Autonomously-by: Codex:GPT-5