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
Constants-only change with no controller runtime or trading behavior; clients opt in when they attach the property to events.

Overview
Adds PERPS_EVENT_PROPERTY.PERPS_MODE (perps_mode) so mobile and extension can tag Perps analytics with Lite vs Pro UI mode ('lite' | 'pro') from a single shared constant.

MODE (mode) is unchanged but documented in code as search intent (discovery / intent / browse), not interface mode, so dashboards are not conflated. Package changelog and eventNames tests cover the new key.

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