Cast v1.4.0

Added

• createAvatarGroup(seeds, options) — compose several member seeds into one cohesive group mark (a clipped mosaic of 1–4 tiles, with extra members collapsing into a +N chip). Great for team/squad/group-DM icons.
• mergeSeeds(...seeds) — combine seeds into a single deterministic, order-independent seed for a stable "pair"/relationship avatar.