[META] Phase 5: Self-serve UI

## Parent

Sub-issue of https://github.com/elastic/obs-integration-team/issues/1048 (Phase 5 — Self-serve UI).

## Goal

Provide a browser-based migration flow so users can migrate without running the CLI directly.

## Target

H2 2026.

## Exit Criteria

- Users can connect or upload source assets through a UI.
- Users can review migration reports and manual-review items in the UI.
- Users can export/import generated Kibana assets from the flow.

## Filing

No program meta exists for UI yet. When this work starts, either add a program under #1048 or parent UI issues here until then. Do not parent them to #30 / #31.