feat: add list WIP limits

[samhuin]

Summary

Adds a polished WIP limit integration for lists.

• Adds a native menu icon for “Edit WIP limit”
• Persists nullable WIP limits on lists
• Exposes wipLimit through board/list API responses
• Normalizes 0 as unlimited
• Keeps WIP limits informative only, without blocking card creation or drag-and-drop

API

The value is exposed as wipLimit, following the existing camelCase API convention.

Semantics:

• null = unlimited
• 0 = normalized to null
• positive integer = active WIP limit

Manual testing

• Create a list without WIP limit
• Set WIP limit to 3
• Reload the board
• Confirm the limit is persisted
• Add more than 3 cards
• Confirm warning/danger state
• Check API response contains wipLimit