Add LLM agent fallback for unmapped tracker patterns

When both pattern matching and domain matching fail to identify a
tracker, an opt-in LLM agent can now attempt identification using
internal database searches and optional web search. The agent returns
structured output (third party name, category, description, confidence)
and the worker auto-creates CommonThirdParty records when needed.

The feature is gated behind the `llm.tracker-mapping.provider` config
field; when unset the worker behaves exactly as before.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/probodconfig/llm_config.go

@@ -49,6 +49,7 @@ type (
 		Probo              LLMAgentConfig               `json:"probo"`
 		EvidenceDescriber  LLMAgentConfig               `json:"evidence-describer"`
 		ThirdPartyAssessor LLMAgentConfig               `json:"third-party-assessor"`
+		TrackerMapping     LLMAgentConfig               `json:"tracker-mapping"`
 	}
 )