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_agent_outputs_topics.py

@@ -0,0 +1,10 @@
+"""AGB muss im LIVE-Pfad verdrahtet sein (_TOPIC_AGENTS), nicht nur per Snapshot."""
+from compliance.api.agent_check._agent_outputs import _TOPIC_AGENTS
+
+
+def test_agb_wired_into_live_topic_agents():
+    assert _TOPIC_AGENTS.get("agb") == "agb"
+
+
+def test_impressum_still_wired():
+    assert _TOPIC_AGENTS.get("impressum") == "impressum"