Introduces the "faux mobile OS" framing: ImplantApp base class,
ImplantNavStack, ImplantAppManifest (app.tres), and ImplantRegistry
autoload. Moddability is a first-class design driver — apps are
droppable directories discovered at startup, main.gd key routing is
manifest-driven, and D-169 primitives stay data-shape agnostic.
Phasing: full pattern lands in the Sprint 36 atlas refactor PR
(#844); Intents dispatcher and DataChannels seam are sketched but
deferred; shipped-build mod discovery stays Phase 6+.
Includes review checklist for #844 and nav-stack edge cases.
jpmschweitzer
be9cfa2fca