Continues the modularization. Moves --gen-zone-readme and
--gen-project-readme into their own translation unit using the
established handle<Family> dispatch pattern. Consolidated the
trailing --out flag parser into a single parseOutFlag helper
(was duplicated between the two handlers).
main.cpp drops 27,736 → 27,445 lines (-291). Behavior unchanged
(verified by re-generating README and PROJECT.md, contents
identical to pre-refactor output).
