#707 Mastodon 4.6.0: Add new Instance properties

[PattaFeuFeu]

Description

This PR adds new properties to the Instance entity as outlined on https://blog.joinmastodon.org/2026/06/mastodon-4-6-for-devs/:

Instance API additions

The GET /api/v2/instance response now exposes several new limits under configuration.accounts that client apps should use, rather than assuming or hard-coding defaults:

max_note_length - maximum bio length
max_display_name_length - maximum display name length
max_profile_fields - maximum number of custom profile fields
profile_field_name_limit and profile_field_value_limit - character limits for field names and values

The server thumbnail object also gains a description field for its alt text.

Next to those, I also checked https://docs.joinmastodon.org/entities/Instance/ and added whatever else had Mastodon 4.6.0.

Relates to: #707

Type of Change

• Enhancement of existing entity

Breaking Changes

None I’m aware of.

How Has This Been Tested?

I ran unit tests

Mandatory Checklist

• I ran gradle check and there were no errors reported
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• All tests pass locally with my changes
• I have added KDoc documentation to all public methods