Bridge a postMessage type to TPEN.eventDispatcher so iframed tools can refresh the page

## Problem

In-document components (e.g. `tpen-transcription-block`) can refresh the simple-transcription view after mutating project data because they share the `TPEN.eventDispatcher` singleton with `simple-transcription` — they dispatch on the bus and `simple-transcription` re-renders.

Iframed splitscreen tools cannot reach that bus. The only channel out is `postMessage`, and `simple-transcription/index.js#handleToolMessages` (line 942) currently only forwards `REQUEST_TPEN_ID_TOKEN` and routes line-navigation message types — there's no handler that lets a tool ask the parent to invalidate cached page data and repaint.

This blocks the JSON-paste fallback flow from refreshing the parent transcription view after a successful page PUT, and would block any future iframed tool that mutates project state.

## Suggestion

Pass the parent current interface in via TPEN_CONTEXT (such as /transcribe). That will give us the ability to know the parent interface, and the child can attempt parent navigation or refresh from there.

or

Pass a message back out from the iframed child that tells the parent to repaint.

When a copy-and-paste fallback succeeds we want to see the data in the interface. There is a cheap hack to force the parent interface to reload right now.