docs: clarify Express pause/resume and Snapshot support

[anycodes]

Description

Express already implements the standard pause/resume and Snapshot API. Clarify that account/region allowlisting and generation2 snapshot admission are prerequisites, rather than a blanket unsupported claim. Add current official links and EN/ZH SDK/CLI examples, connect-based resume, request-timeout and safe-cleanup rules.

Original request:reconcile the current implementation with https://help.aliyun.com/zh/agent-sandbox/e2b-sdk-compatible-api-list . Existing real generation2 acceptance remains in the immutable owner record; this prose-only change does not claim a new cloud run or enable unimplemented native Provider features.

Type of Change

• Documentation

Changes

• Identify actual standard public entry points and their separate native extension contract.
• Explain allowlisting, Snapshot generation2 requirement, name conflicts, memory-only restrictions and independent resource ownership.
• Include owner process note/evidence, EN/ZH guide and Unreleased entry. Preserve historical evidence and unrelated local contributor drafts.

Testing

• Examples parse; relative links resolve; installed CLI help confirms each documented command
• Repository health/hygiene and diff checks
• Actual Python sync/async symbol signatures checked in a fresh paired source install
• Current-head hosted gates before merge

Definition of Done

Documentation-only checks follow workspace contributor scope. Existing real SDK5/CLI2 conditional acceptance is cited as history, not rerun or relabeled. No cloud/model credentials or tests are added to Actions. Standard runtime and vendored implementation are unchanged.