[ER-332] US1 - Update Link Previews (Web first) | External

### Your use case

We’re building an updated URL preview system to provide a consistent, privacy-forward link experience. This work introduces reliable previews for public links across all rooms (unencrypted and encrypted), and lays the groundwork for richer link interactions in the future.

This ticket will externally track the work.

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# Overview

Today, links shared in chats can be hard to scan, or require leaving the conversation to understand where they lead. This project provides preview data so users can quickly understand shared links.

The goal is to deliver consistent previews in **encrypted and unencrypted rooms**. With clear **visibility of link destinations**

## Baseline URL Previews (All Users)

When a user shares a public URL, Element can display a preview that includes:
* The plain URL (visible)
* Page title
* Description (if available)
* Thumbnail (if available)

If metadata is missing, unsafe, or requires authentication:
* The system falls back to **showing the plain URL only**.

Previews should work in Encrypted rooms & Unencrypted rooms
Previews should be toggle-able -- Users go to Settings to disable them
Users can also dismiss previews locally without changing the original message

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### Phase 1 — Consistent URL Previews

Deliver a consistent preview experience for links
* URL previews available and works in encrypted and unencrypted rooms
* Plain URL remains visible
* Graceful fallback to plain URLs when preview cannot be generated
* User controls for enabling/disabling previews
* Close/dismiss preview control

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# Current Status

Work is beginning
We’ll update this ticket as milestones are reached and when phases move forward.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_