Cannot log into LOCAL_DOMAIN when it differs from WEB_DOMAIN

**Describe the bug**

- Which site: dev.phanpy.social, phanpy.social, and phanpy.blaede.family
- Which instance: (mastodon.)blaede.family

**To Reproduce**

Steps to reproduce the behavior:
1. Go to log into Phanpy
2. Enter `blaede.family` as the instance
3. See the "Failed to log in" error

**Expected behavior**

Since my instance is set up with `blaede.family` as the LOCAL_DOMAIN according to [the Mastodon docs](https://docs.joinmastodon.org/admin/config/#federation), I would like to be able to log in with that instead of requiring the full `WEB_DOMAIN` of `mastodon.blaede.family`

**Desktop (please complete the following information):**

- OS: Endless OS (but it doesn't change based on the OS 😉)
- Browser: Firefox, but same behavior in Chrome
- Version: 119

**Smartphone (please complete the following information):**

- Device: Pixel 7
- OS: Android 14
- Browser: Firefox
- Version: 119