feat(agb): wire validated routed AGB engine into live check path

Consolidate the AGB C-lean engine (71% FP -> ~0, validated vs 7-company
Opus GT) onto the canonical checker library and into the live check path.

- AGBAgent.evaluate now runs routed C-lean: keyword (L1/L2) -> business-
  model gate -> per-item decision_method routing (embedding/reference/llm
  via services/checkers/) -> severity re-tiering (LOW -> recommendation),
  honoring context.skip_llm.
- New agb/_pipeline.py orchestrates the routing; agent.py stays thin.
- Remove the 3 AGB-local checker duplicates (_reference_check,
  _embedding_rescue, _llm_judge); services/checkers/ is now canonical.
- Wire "agb" into _agent_outputs._TOPIC_AGENTS so the live check emits a
  validated AGB tab (was snapshot-only).
- Run topic agents concurrently (asyncio.gather) + emit each tab via SSE
  as it finishes -> progressive results, no wait on the slowest agent.
- Tests: checker units (mocked), routed agent (gate/rescue/re-tier),
  topic wiring; existing AGB tests made offline-safe.

dev-only, no deploy.

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

backend-compliance/compliance/tests/test_agb_agent.py

@@ -1,12 +1,27 @@
-"""AGBAgent — kuratierte §§-305-ff-BGB-Checkliste (ChecklistAgent-Subclass)."""
-
-from __future__ import annotations
-
+"""AGBAgent (v2, routed). Embedding/LLM offline-gestubbt → kein Netzwerk."""
 import asyncio
 
+import pytest
+
+import compliance.services.specialist_agents.agb._pipeline as pipeline
+from compliance.services.checkers.base import CheckResult
 from compliance.services.specialist_agents import REGISTRY, AgentInput
 
 
+class _Stub:
+    def __init__(self, present):
+        self._p = present
+
+    async def check(self, ctrl, doc):
+        return CheckResult(present=self._p)
+
+
+@pytest.fixture(autouse=True)
+def _offline(monkeypatch):
+    monkeypatch.setattr(pipeline, "_EMB", _Stub(None))
+    monkeypatch.setattr(pipeline, "_LLM", _Stub(None))
+
+
 def _run(text: str):
     return asyncio.run(
         REGISTRY.get("agb").evaluate(AgentInput(doc_type="agb", text=text)))