feat(v0.4.0): vNext — closed-loop world model + settlement contract

Implements the vNext architecture from the research doc: demote the noisy
multi-rail planner in favour of a closed loop (world truth → invariant check)
plus a single utility-driven goal authority.

L1 services (fix no_drop / silent pathfinder hang first):
- InventoryLedger: diff-based "did I actually get it" verifier; acquire-food
  now confirms via ledger.gainedSince instead of the unreliable count/event.
- MotionService.gotoSafe: wall-clock timeout + progress watchdog +
  path_update(noPath/timeout) → structured {reached|stuck|timeout|nopath}.

L3 plan — unify the three competing rails (curriculum/manifesto/storyline):
- Settlement Contract: ordered M0–M9 milestones, each invariant-checked
  against an authoritative world view (early steps delegate to the proven
  curriculum; late game adds farming).
- InvariantChecker + predicate library; GoalManager selects the lowest unmet
  milestone via utility argmax (food-urgency preempts, DEPS-style).
- Wired into the scheduler: bot.js precomputes snapshot.contract; reflex.js
  consumes it in place of the storyline rail. Manifesto L0 still preempts.

Eval + robustness:
- Village Score (single 0..1 metric) on the snapshot + TUI "build" line.
- survive.dig-in skill + dusk_dig_in mode (exposed at night, no bed → cover).
- approach_block helper (GoalNear + lookAt, avoids GoalLookAtBlock #341).

+28 new tests (450 total green). LLM remains entirely off the tick path.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

runtime/skills/index.js

@@ -30,6 +30,7 @@ import { skill as flee } from "./flee.js";
 import { skill as sleep } from "./sleep.js";
 import { skill as tunnelOut } from "./recovery-tunnel-out.js";
 import { skill as pillarUp } from "./pillar-up.js";
+import { skill as digIn } from "./dig-in.js";
 import { skill as escapePitSafe } from "./escape-pit-safe.js";
 import { skill as diagPhysics } from "./diagnose-physics.js";
 import { skill as diagScan, matchSkill as diagMatch } from "./diagnose-scan.js";
@@ -77,6 +78,7 @@ register(flee);
 register(sleep);
 register(tunnelOut);
 register(pillarUp);
+register(digIn);
 register(escapePitSafe);
 register(diagPhysics);
 register(diagScan);