feat(perps-controller): add perps_mode analytics property for Lite/Pro UI

[michalconsensys]

Explanation

Clients need to attribute Perps analytics events by Lite/Pro interface mode ('lite' | 'pro'). Search already uses PERPS_EVENT_PROPERTY.MODE (mode) for search intent (discovery / intent / browse), so reusing that key would collide and break dashboards.

This PR adds PERPS_EVENT_PROPERTY.PERPS_MODE = 'perps_mode' in @metamask/perps-controller so mobile and extension can import a single shared key for Lite/Pro UI mode. Existing MODE is left unchanged and clarified with a comment. Tests and the package changelog are updated accordingly.

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Additive analytics constant only; no runtime or breaking API changes beyond a new optional event property key.

Overview
Adds a shared analytics property key so mobile and extension can tag Perps events with Lite vs Pro UI mode without reusing search’s mode field.

PERPS_EVENT_PROPERTY.PERPS_MODE (perps_mode) is introduced for values 'lite' | 'pro'. MODE (mode) is unchanged and documented as search intent only (discovery / intent / browse). Changelog and unit tests cover the new export.

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