## What changed
- restore the desktop invoicing-period category groups as a vertical
right-hand rail
- use a 3:1 content-to-navigation split at desktop widths with
responsive stacking below 1024px
- size the inline month selector to the available content width with a
readable 32rem cap
- adapt the invoice review workspace to the narrower content region
- add unit contracts and browser geometry coverage for desktop, tablet,
and mobile
## Why
The grouped period categories had moved into a wide horizontal row,
leaving unused space on the right and constraining the period content.
The inline month picker was also too small to read comfortably.
## User impact
Superusers again see period categories in the right rail on desktop.
Compact layouts retain responsive navigation, and the review/object-tree
content avoids field wrapping when the main region becomes narrow.
## Validation
- 60/60 focused unit tests
- 30/30 full Chromium desktop invoicing-period browser tests
- 9/9 priority browser tests across Chromium desktop, tablet, and mobile
- ESLint
- production Vite build
- focused Prettier checks
- git diff check
Jeppe B
1768f5a38e