fix: preserve firefoxId from dynamically detected extensions

[austingray]

Summary

This PR fixes Firefox extension detection for dynamically detected wallet extensions by properly preserving the firefoxId property throughout the SDK.

The Problem:
When a browser extension responds to the SDK's ping message with a firefoxId in the sender object (indicating it's a Firefox extension), the SDK was not preserving this property. This caused the "Use Extension" button to fail on Firefox because the SDK couldn't identify the extension properly.

Changes:

• beacon-types/Extension.ts: Added firefoxId optional property to the Extension interface
• beacon-transport-postmessage/PostMessageTransport.ts: Capture firefoxId from pong responses in listenForExtensions()
• beacon-ui/utils/wallets.ts: Updated mergeWallets() to use explicit firefoxId property from detected extensions
• beacon-ui/hooks/useWallets.tsx: Pass through firefoxId for dynamically detected extensions
• beacon-ui/hooks/useConnect.tsx: Fixed setInstallState() to show install screen for extension-only wallets

Test plan

• Tested with a custom Firefox extension that provides firefoxId in pong response
• Verified extension appears in wallet list with "Use Extension" button
• Verified clicking "Use Extension" properly sends pairing request to extension
• Verified backwards compatibility - extensions without firefoxId continue to work

[lukeisontheroad]

Thanks for the PR! We've actually already partially addressed this in our 5.0.0-beta branch - the UI layer already has firefoxId support for wallets in our static list.

However, you're right that we're missing the dynamic discovery piece (capturing firefoxId from the pong response in PostMessageTransport). We'll review your implementation and adopt the missing parts.

In the meantime, to get your wallet listed officially, please open a PR to our wallet registry: https://github.com/airgap-it/beacon-wallet-list

Is your extension already released? We'd be happy to test it if you can share a link or point us to where we can install it.

[austingray]

Hey, awesome news. My wallet isn't ready to be released and my number one priority is supporting firefox since there are no tezos firefox browser wallet extensions available. It's open-source and available for review here https://github.com/austingray/tm-wallet. Once I get it to a more publishable state I will most certainly be opening a PR for it to be added to the registry. Thank you so much.

[austingray]

did some cleanup and removed some hacking about with icons i was doing