Desktop app hands links to itself over to the OS browser when the host is spelled `localhost` or `[::1]`

## Description

The desktop window loads http://127.0.0.1:port, and the external-navigation check (apps/desktop/src/externalNavigation.ts) treats any URL whose origin string differs as external and opens it via the OS. But the loopback host has three spellings (localhost, 127.0.0.1, [::1]), so a link to the app itself written as http://localhost:port opens the default browser onto the app's own address instead of staying internal.

## Steps to reproduce

1. Launch the desktop app
2. Find its port via `lsof -nP -iTCP -sTCP:LISTEN | grep bun`, get a clickable http://localhost:port/ link inside the app (e.g., ask the agent to reply with exactly that markdown link), click it.

## Expected behavior

internal link

## Actual behavior

the OS browser opens onto the app's own host

## Environment

- OS: macOS
- Bun version (`bun --version`): 1.4.0
- Node version (`node --version`): v26.8.1
- ThinkRail version / commit: 756a4b8e0bff94a36565e354c511f2b3bf353fd6

Start with apps/desktop/src/externalNavigation.ts and reproduce the issue using a clickable http://localhost:port/ link after finding the port with the documented lsof command. Check how the navigation check compares loopback host spellings, then verify that links using localhost, 127.0.0.1, and [::1] stay internal while external links still open through the OS browser.

Written by the indexing model from the issue text.