release: v0.15.1.0.1 — classify the LangGraph gateway under the backend architecture policy

[rrrozhd]

Brings zeroth.core.langgraph_gateway (14 modules) under the backend dependency policy.

• Five longest-prefix mappings in LEGACY_DOMAIN_PREFIXES: the package root (and its service-plane modules, including the new enforcement/enforcement_store) → service; models/inventory → contracts; capabilities/events → governance.
• The two real cross-domain reuses this exposes are documented as exact TEMPORARY_EXCEPTIONS entries, each with a removal task tied to the gateway relocation phase (ZER-24): the governance decision service's reuse of the admission orchestrator, and the LangGraph integration client's reuse of the enforcement surface.
• Regression tests: expected domain for the package root and all 13 submodules, an exact pin of the 5-entry mapping set, an on-disk classification walk, and an exact assertion of the two documented edges (scan run without exceptions).
• Version 0.15.1.0.1 synced across pyproject, uv.lock, CHANGELOG, frontend version pins, and the release-metadata tests.

Full suite green locally in the pre-commit gate: 5812 passed, 4 skipped.