plan: phase 1 engine core (engine-first phasing)

Replaces the deleted vertical-slice plan. P1 ships scaffold + full
deterministic engine (types, balance, rng, state, orders, combat,
defence/build/propaganda/wooing/launch/final-retaliation phases, all 4
win conditions, resolution orchestrator, reducer) verified entirely
through Vitest. No UI, no AI personalities — they land in Phases 3
and 2 respectively.

19 tasks, TDD-structured. End-of-phase verification: npm run test:run.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: emp3thy