chore: rename collab feature flag key to multi_agent

[jif-oai]

Summary

• rename the collab feature key to multi_agent while keeping the Feature enum unchanged
• add legacy alias support so both "multi_agent" and "collab" map to the same feature
• cover the alias behavior with a new unit test

[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

codex/codex-rs/core/config.schema.json

Lines 1327 to 1329 in 48401ae

	"collab": {
	"type": "boolean"
	},

Regenerate config schema to include multi_agent

The feature key was renamed to multi_agent in FEATURES, but the checked-in schema fixture still advertises only collab here. This leaves editor/schema consumers out of sync (new key appears invalid or missing) and will drift against features_schema generation/tests.

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[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".