Each per-feature LLM ability is now a self-contained module in
server/abilities/ with its own Ability<K> const (schema line, constraint
bullet, validator, applier, isMeaningful, stub default, user-payload
field). The ordered ABILITIES registry (index.ts) assembles them in the
canonical order: takeovers → wars → hybrid → economy → industry → nuclear
→ leaders → ideology.
All function bodies are moved VERBATIM from engine.ts. The engine is
untouched in this commit — P4 will rewire it to use the registry.
