feat: replace X-space banner with latest newsletter update banner

[m4r1m0]

Description

Replaces the X-Space event banner in the top-right corner of the app with a "latest update" banner that links to the newest Tari newsletter published on https://tari.com/updates.

Motivation and Context

The top-right banner previously promoted X Space events via the airdrop backend. It now links to the latest Tari newsletter instead, always showing the newest one without an app update: the backend fetches the updates listing hourly, detects changes, and pushes them to the UI automatically via a Tauri event.

How Has This Been Tested?

• pnpm lint (eslint + knip + tsc) passes
• pnpm test — 1054 tests pass (X-space store test cases removed)
• cargo fmt --check passes; new Rust module compiled, clippy-clean, 3 unit tests for the HTML parser pass
• Rust module live-tested against https://tari.com/updates (returns https://tari.com/updates/2025-02-14-update-142 / "Obeisance of the Ootle")
• Full cargo check of the Tauri crate still to run on a machine with GTK dev libraries installed

What process can a PR reviewer use to test or verify this change?

1. Run the app (pnpm tauri dev)
2. Confirm the top-right banner shows "NEW UPDATE" + the latest newsletter title and opens the article in the browser on click
3. Publish a new entry on tari.com/updates (see caveat below) and confirm the banner updates within ~1 hour without an app restart

Caveat

The banner resolves the latest update by parsing https://tari.com/updates, which lists entries from the _updates/ collection of the tari-dot-com website repo. The newsletter must be published as a new entry on that page for the banner to pick it up. This is also documented in src-tauri/src/latest_update.rs.

Breaking Changes

• None
• Requires data directory on base node to be deleted
• Requires hard fork
• Other - Please specify

[m4r1m0]

I did it this way because it was quickest and only required updating Tari Universe as opposed to updating the website first and then updating Tari Universe.

But if there's time, or in the future, it might be best to add an RSS feed to the website and pull the newsletters to TU that way