Add semantic pre-filter for GraphRAG edge scoring (#702)

Embed edge descriptions and compute cosine similarity against grounding
concepts to reduce the number of edges sent to expensive LLM scoring.
Controlled by edge_score_limit parameter (default 30), skipped when edge
count is already below the limit.

Also plumbs edge_score_limit and edge_limit parameters end-to-end:
- CLI args (--edge-score-limit, --edge-limit) in both invoke and service
- Socket client: fix parameter mapping to use hyphenated wire-format keys
- Flow API, message translator, gateway all pass through correctly
- Explainable code path (_question_explainable_api) now forwards all params
- Default edge_score_limit changed from 50 to 30 based on typical subgraph
  sizes

trustgraph-base/trustgraph/schema/services/retrieval.py

@@ -15,6 +15,7 @@ class GraphRagQuery:
     triple_limit: int = 0
     max_subgraph_size: int = 0
     max_path_length: int = 0
+    edge_score_limit: int = 0
     edge_limit: int = 0
     streaming: bool = False