p3: map Brave LLM Context; RRF merge; per-source no_rerank

Live llm/context hits live in grounding.generic plus a URL-keyed
sources map, not a sources array. Fan-in uses reciprocal-rank fusion
instead of cosine. no_rerank keeps that source's own order as a prefix.

internal/search/build.go

@@ -35,6 +35,16 @@ func Build(cfg config.Search, cache *dcache.DB, emb Embedder, log *slog.Logger)
 		Embedder:  emb,
 		Log:       log,
 		TavilyCap: cfg.Tavily.DailyCreditCap,
+		NoRerank:  map[string]bool{},
+	}
+	if cfg.SearxNG.NoRerank {
+		e.NoRerank[NameSearxNG] = true
+	}
+	if cfg.BraveLLM.NoRerank {
+		e.NoRerank[NameBraveLLM] = true
+	}
+	if cfg.Tavily.NoRerank {
+		e.NoRerank[NameTavily] = true
 	}
 	if cfg.SearxNG.Enabled {
 		u := cfg.SearxNG.URL