When a workspace has a single account, publish controls aren't clear

[kurucu]

Steps to reproduce the problem

1. Start a new workspace
2. Add a single account (e.g. X)
3. Draft a post

Expected behaviour

The one account should be pre-selected, pop-up allows selection when post/queue is selected, or a useful warning shown

Actual behaviour

Posting controls are disabled with no warnings

Detailed description

When drafting a post (especially as a new user) it's not clear on what's going on. They should be either:

• provided with either automatic selection of their only account;
• the ability to select account(s) when posting/queueing (which would be useful for all use-cases, one account or many); or,
• a label telling the user to choose an account, rather than just disabled controls.

Specifications

Mixpost v1.7.2