abc78cd071
Zero behavior change: \`public class\` -> \`public partial class\`. Each functional area (Scenes, Background, Webcam, Audio, Trax, Socials, Streaming, Chat, Overlays, Account, License) will move to its own file next, one commit per partial — each a roll-back point. Docs updated in the same commit: ViewModels/index.md (split map), ai.md (architecture table), HANDOFF.md (state). verify.sh: build 0 warnings, only the 2 known pre-existing test failures.