feat: add GPT-5.5 to Codex subscription and Anton API

[OmGuptaIND]

Summary

• Adds gpt-5.5 to the Codex harness subscription menu (shows up alongside GPT 5.4, 5.4 Mini, O3)
• Adds gpt-5.5 to the Anton/GRU API-key model catalog with cost + context metadata
• Registers 1M context window in compaction.ts so compaction uses the right budget

Test plan

• Open the model selector → GPT 5.5 appears under Subscriptions (ChatGPT Codex)
• Open the model selector → GPT 5.5 appears under Your API keys (Anton)
• Select GPT 5.5 and send a message — session resolves the model correctly
• Verify the "balanced" tag + "Long context · flagship" note render

Note: cost is set to $3 / $18 per 1M tokens as a placeholder (slight bump over 5.4). Update with actual pricing when available.

🤖 Generated with Claude Code