refactor(#74) P3: add the 8 ability modules + ABILITIES registry

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.

server/abilities/index.ts

@@ -0,0 +1,127 @@
+// The ordered LLM-ability registry.
+//
+// `ABILITIES` is the single source of truth for the 8 per-feature LLM abilities.
+// The engine iterates it in this order:
+//   takeovers → wars → hybrid → economy → industry → nuclear → leaders → ideology
+// for (a) the system-prompt schema lines + constraint bullets, (b) the per-ability
+// validate calls inside validateTurnResult, (c) the payload fields in buildUserPrompt,
+// (d) the ordered apply block inside applyTurnResult, (e) the isMeaningful check,
+// (f) the runTurn unclear-fallback defaults, (g) the stub's deterministic fields, and
+// (h) the db.ts state-field migrations.
+//
+// Each ability file defines its own `Ability<K>` const (the schema line, constraint
+// bullet, validator, applier, meaningfulness predicate, stub default, and user-payload
+// field). This module assembles them into the ordered `ABILITIES` array and re-exports
+// every public name the engine (and its tests) need.
+
+import { takeovers } from './takeovers';
+import { wars } from './wars';
+import { hybrid } from './hybrid';
+import { economy } from './economy';
+import { industry } from './industry';
+import { nuclear } from './nuclear';
+import { leaders } from './leaders';
+import { ideology } from './ideology';
+import type { Ability, AbilityField } from './types';
+
+/**
+ * The 8 per-feature LLM abilities in their canonical apply order.
+ * The order matters: it determines the order of the schema lines in the
+ * system prompt, the order of the validate calls, the order of the apply
+ * steps, and the order of the payload fields in the user prompt.
+ */
+export const ABILITIES: readonly Ability<AbilityField>[] = [
+  takeovers,
+  wars,
+  hybrid,
+  economy,
+  industry,
+  nuclear,
+  leaders,
+  ideology,
+];
+
+// ── type re-exports ────────────────────────────────────────────────────────────
+
+export type {
+  Ability,
+  AbilityCtx,
+  UserPromptCtx,
+  AbilityField,
+} from './types';
+
+// ── shared helpers ─────────────────────────────────────────────────────────────
+
+export {
+  resolveNationRef,
+  resolveRegionKey,
+  freshNationId,
+  freshWarId,
+  NEW_NATION_STATS,
+} from './shared';
+
+// ── war helpers ────────────────────────────────────────────────────────────────
+
+export {
+  activeWarPairs,
+  atWar,
+  syncWarRelations,
+} from './apply-helpers';
+
+// ── takeovers ──────────────────────────────────────────────────────────────────
+
+export {
+  validateTakeovers,
+  applyTakeover,
+} from './takeovers';
+
+// ── wars ───────────────────────────────────────────────────────────────────────
+
+export {
+  validateWarOps,
+  applyWars,
+} from './wars';
+
+// ── hybrid ─────────────────────────────────────────────────────────────────────
+
+export {
+  validateHybridOps,
+  isHybridOpType,
+  HYBRID_STAT_EFFECT,
+  shiftRelationTowardHostile,
+  applyHybridOp,
+} from './hybrid';
+
+// ── economy ────────────────────────────────────────────────────────────────────
+
+export {
+  validateEconomyOps,
+  applyEconomyEffects,
+} from './economy';
+
+// ── industry ───────────────────────────────────────────────────────────────────
+
+export {
+  validateIndustryOps,
+  isIndustryType,
+  applyIndustryEffects,
+} from './industry';
+
+// ── nuclear ────────────────────────────────────────────────────────────────────
+
+export {
+  validateNuclearOps,
+  applyNuclearOps,
+} from './nuclear';
+
+// ── leaders ────────────────────────────────────────────────────────────────────
+
+export {
+  validateLeaderOps,
+} from './leaders';
+
+// ── ideology ───────────────────────────────────────────────────────────────────
+
+export {
+  validateIdeologyOps,
+} from './ideology';