feat(intern-decision-serve): Intern-Decision-4B behind semif-serve's HTTP surface

Contract, service and tests (fake engine, no GPU). Scores through the checkpoint's own
inference.py (DecisionEngine.predict, sha256-pinned); maps semif decisions onto Jev choice
questions, packs /decide/shared into calls of at most 16, runs orderings in waves, and keeps
semif's error mapping, admission, body limit and hard VRAM cap. Deltas from semif-serve are
listed in the contract.

services/intern-decision-serve/.dockerignore

@@ -0,0 +1,6 @@
+*
+!pyproject.toml
+!uv.lock
+!src/
+**/__pycache__
+src/*.egg-info