Add mods/sdk/ with the kindred_sdk Python package providing a stable
API layer for addon integration with Kindred Create platform features.
Modules:
- context: editing context/overlay registration wrappers
- theme: YAML-driven palette system (Catppuccin Mocha)
- origin: FileOrigin registration helpers
- dock: deferred dock panel registration
- compat: version detection utilities
The SDK loads at priority 0 (before all other addons) via the existing
manifest-driven loader. Theme colors are defined in a single YAML
palette file instead of hardcoded Python dicts, enabling future theme
support and eliminating color duplication across addons.
Closes#249
