feat: [STELLAR] dormant foundation plumbing (1/3)

[khanti42]

Description

Changes

• Adds Stellar/XLM constants, asset mappings, account types, network metadata, icons, and block explorer configuration.
• Registers Stellar wallet Snap references for future Snap-based account creation.
• Adds Stellar-aware account, network, bridge, swaps, balance, and send-flow handling.
• Adds Stellar address and asset ID validation helpers.
• Adds tests covering Stellar accounts, assets, balances, network selectors, and recipient validation.
• Temporarily pins required core packages to preview releases.

Important

This PR must not be merged until the real releases of the core packages are available. The current package changes rely on @metamask-previews/* versions and should be replaced with official package releases before merging.

Testing

• Added/updated unit tests for the prepared Stellar flows.

Changelog

CHANGELOG entry:

Related issues

Fixes:

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

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[khanti42]

remove testnet

[khanti42]

remove testnet

[stanleyyconsensys]

is it needed for now?