Move the pure-header utilities shared by app/ and engine/ out of
engine/common/ into a new shared/include/oakutil/ layer (define, lerp,
decibel, digit, range, crashpadutils, autoscroll, qtutils, filefunctions
declarations, and a trimmed xmlutils exposing a CancelAtom-free void*
overload). engine/common/ keeps forwarding headers so internal include
paths are unchanged; app/ now includes oakutil/* directly.
engine/node/project.h gains an explicit NodeGroup forward declaration
previously obtained transitively through the old xmlutils.h.
Move the finished migration campaign docs (handoffs v3-v6, roadmap,
R5 guides, R6 cleanup, R7 pure-ABI) from docs/zh/ into
docs/zh/plans/completed/ with an archive README; fix all
cross-references; refresh plans/README.md index (active plans now
marked unlocked).
Complete documentation set for the facade migration (B1-R6) and beyond:
facade-migration-roadmap, handoffs v3-v6, R5 guides, R6 cleanup plan,
R7 pure-ABI plan, long-term plans (riir/ai-agent/gtest/ui-redesign),
updated Chinese README draft, UI design mockups, and the Google Test +
struct-typedef rules in CONTRIBUTING.
Mike-Solar