Document two-domain connection profile proposal

[poulcarlsen53]

What changed

This adds a short maintainer-facing proposal for supporting two server domains inside one WhiteDNS connection profile.

The doc lays out:

• the current single-domain shape in ConnectionProfile, StormDnsServerProfile, generated TOML, profile links, and runtime launch storage
• the key product question: whether both domains share the same encryption key/method, or whether this really needs a multi-endpoint server model upstream
• a small app-layer path for the shared-key case using the existing TOML DOMAINS = [...] array
• the profile editor behavior, import/export compatibility, tests to add, and an interim guide for users today

Why

The current workaround is to create two separate connection profiles for what may be one logical server. That works, but it duplicates profile management and makes primary/backup domains feel heavier than they need to be.

I kept this as a proposal instead of a schema change because the encryption model needs maintainer confirmation first. If domains can have separate keys or methods, the app should not fake that by adding a second text field; it should wait for a proper upstream-supported endpoint format.

Validation

• git diff --check

No Gradle run for this one because it only adds documentation.