Signup refactoring follow-ups

[jeriox]

bugs

• [x] fallback method fails with "shift state render failed"

missing "secondary" code

• [ ] API integration for complex structure
• [ ] complex (and maybe other structures) missing get_signup_info implementations for log and pdf export
• [x] tests for complex structure and holes in current coverage

deployment/setup stuff

• [ ] production vue
• [ ] better solution for CSP exempt vues

UI/features

• [x] add button to signup blocks to menu
• [ ] stuff from https://github.com/orgs/ephios-dev/projects/5

Signup Design

• [ ] discuss the ensemble as a whole and fix inconsistencies with it
• [ ] request flow: optionally don't allow request if shift is full to lower disposition workload
• [x] complex display: correct "fullness" detection with a matching algorithm supporting disposition decisions
• [ ] matching algorithm support for "at least one in group is qualified as"
• [ ] add user documentation