v1.3.0

Adds custom creatures: DM-authored homebrew monsters that sit alongside the Open5e library everywhere a creature is used.

• Create a creature from a blank form or by copying ("reskinning") an existing library or custom one, with the curated statblock field set and repeatable trait/action/attack rows.
• Custom creatures show up in the library browser (with a "Custom" badge and source filter), the statblock panel, live encounters, and saved encounter presets — exactly like library creatures, including edit and delete controls.
• A saved preset still reaches a custom creature the same way it reaches a library one: add it to the board, then "Save current" — a preset stays composition, not a snapshot.
• Deleting a custom creature that's still on the board or in a saved preset now succeeds cleanly instead of erroring mid-apply, and a combatant left pointing at a deleted creature reads "Creature unavailable" instead of a misleading "Nothing selected".

Docker image: ramongebben/kernel-dm-toolbox:latest (also tagged 1.3.0, 1.3, main).