Analyse how the 53 modules currently collaborate and why none of them can be
trimmed outside the hardcoded WASM axis, then lay out a target architecture and
a six-step route to per-module build options.
Adds scripts/module_depgraph.py, which produces the dependency graph, the
7-layer topological ordering and the cycle list the document cites. Its --check
mode fails on any back-edge outside the 16 known ones, so it doubles as the CI
guardrail for step S1.
Co-authored-by: 西风逍遥游 <sunxfancy@gmail.com>