chore: add CODEOWNERS — joshsiv-mulga gates network/ + vpcd/

Fall-through reviewer for any change is the maintainer.
network/ and vpcd/ are explicitly listed so the matching branch
protection rule ("Require review from Code Owners") routes those
PRs to joshsiv-mulga. Those trees are governed by ADR-0006
invariant tests (spinifex/network/invariants/); CODEOWNERS adds a
human review gate on top of the mechanical fence.

Refs: mulga-siv-141

.github/CODEOWNERS

@@ -0,0 +1,17 @@
+# CODEOWNERS — GitHub PR review enforcement
+#
+# Format: <path pattern>  <owner> [<owner> …]
+# Order matters — last matching pattern wins.
+#
+# Set the matching branch protection rule on `dev` and `main` to
+# "Require review from Code Owners" or this file is advisory only.
+
+# Fall-through: any change needs a maintainer review.
+*                           @joshsiv-mulga
+
+# Network layer is governed by ADR-0006 invariant tests.
+# Changes here must respect those clauses — see
+# spinifex/network/invariants/ and
+# docs/development/proposals/az-local-architecture/0006-spinifex-network-layer-contract.md
+/spinifex/network/          @joshsiv-mulga
+/spinifex/vpcd/             @joshsiv-mulga