Surveys: honor appearance.position (currently bottom-only)

Problem

posthog-react-native 4.43.13 (PostHog/posthog-js#3498) added support for honoring appearance.position on all 9 SurveyPosition values (top_left, top_center, top_right, middle_left, middle_center, middle_right, left, center, right). Survey UI on iOS still renders bottom-only regardless of the configured position.

This means surveys created in the PostHog UI with a custom position will not visually match what users see on iOS, breaking parity with the web SDK and React Native.

Expected behavior

Honor appearance.position in the iOS survey UI, matching the web SDK semantics:

• top_* → anchored to top edge
• middle_* → vertical middle
• left / center / right (no prefix) → anchored to bottom edge

Reference

• React Native implementation: https://github.com/PostHog/posthog-js/pull/3498
• Feature parity table: https://github.com/PostHog/posthog/blob/master/frontend/src/scenes/surveys/surveyVersionRequirements.ts

Start by locating the Android survey UI code that currently renders surveys at the bottom and trace how appearance.position is read. Compare the behavior with the referenced React Native implementation, then verify all nine SurveyPosition values use the documented top, middle, or bottom anchoring semantics.