fix(mobile): Preserve context through Android clipboard bridges#98

What Changed

On Android, the composer clipboard module keeps the most recent copied T3 context fragment in memory. When a later paste finds the same text without the HTML marker that carries the structured context, the editor restores that fragment and imports the context the normal way, with fresh context and attachment identities. A different clipboard item discards it, Paste as Text stays plain, and the copy lasts only for the app process.

Why

Copying a sent message that has an image and pasting it into the composer showed the image chip as unavailable when something between copy and paste kept the text but dropped the HTML, such as Waydroid's host clipboard bridge or a clipboard manager that rewrites HTML. The pasted t3-context:// reference then had no context record to bind to. This also happens on upstream main.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes