[codex] inject sealos context only on first gateway session turn

[Che-Zhu]

Summary

• inject Sealos deploy context only on the first turn of a Codex gateway session
• move prompt augmentation into the shared gateway runner so both chat-v2 and legacy gateway turn paths behave the same
• keep persisted task messages unchanged by sending the raw user message through storage and conditionally augmenting only the gateway prompt

Root Cause

The app was prepending Sealos deploy context on every user turn before sending prompts to the gateway, which caused follow-up messages in the same session to carry repeated context.

Validation

• pnpm format
• pnpm format:check
• pnpm type-check
• pnpm lint (existing repository warnings only)
• manual runtime verification that only the first turn in a session includes the Sealos context