feat: add support for detecting links in messages and opening them in the default browser

[nexxai]

Summary

I've implemented the detection of URLs in messages so that a user can quickly open them with their browser.

Why

When someone posts a link or multiple links in a message, I'd like to be able to open them.

How

In the "Message actions" window, I have added the "Open URL" option with the current shortcut key o (the lowercase letter O). If only a single URL is detected in the message, the o key immediately opens the URL in the browser. If multiple links are detected, it will open a submenu where the first 10 messages are available via the shortcut keys of 1-0, and the rest must simply be scrolled to.

I also added some simple highlighting of URLs to make them more obvious.

Testing

• cargo fmt --all --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --all-features
• Manual test in a real terminal (describe below)

Terminal: Ghostty (latest)
OS: macOS Tahoe 26.5

Screenshots or recordings

URLs being detected and highlighted in message:

Actions menu showing how many URLs were detected:

Actions sub-menu showing detected URLs and hotkeys for quick access:

Checklist

• One logical change per PR.
• No tokens, passwords, MFA codes, or raw auth bodies in code, tests, or logs.
• Change does not add self-bot automation, mass actions, or scraping.
• Updated README.md, if behavior or workflows changed.

[nexxai]

This PR replaces #72

[chojs23]

Could you please rebase this and update the key handling and shortcut labels to follow the new KeyBindings structure?

[nexxai]

@chojs23 I've rebased and updated the key handing/shortcut labels as requested