cstage cmd/w6c/cgen.c gained the missing N_DOT N_INDEX-lhs branch.
Covers both [N]*Struct and [N]Struct via fldloadop. wwstage already
handled [N]*Struct since 7c75dd2; refactored to mirror cstage exactly
and added [N]Struct. The spill workaround in dotchainresolve stays
(Pike rule); task #14 retires it as a follow-up.
Wwstage cgassign N_DOT(N_INDEX,...) silent store-drop discovered in
scope, filed as task #16.