perf(agent): cache lowercased entity names and early-exit in resolve_or_create

resolve_or_create allocated a fresh lowercased String for every entity
on every call (this runs per extracted mention during entity/relation
extraction) and never short-circuited on an exact dist == 0 match,
scoring every remaining entity regardless. Add Entity::name_lower,
computed once at construction (add_entity, and schema.rs's direct-push
load path), and break out of the scan as soon as an exact match is
found.

INT-12

crates/clawhdf5-agent/src/schema.rs

@@ -480,6 +480,7 @@ fn load_knowledge_group(file: &clawhdf5::File) -> Result<KnowledgeCache, MemoryE
             cache.entities.push(crate::knowledge::Entity {
                 id: entity_ids[i] as u64,
                 name: entity_names[i].clone(),
+                name_lower: entity_names[i].to_lowercase(),
                 entity_type: entity_types[i].clone(),
                 embedding_idx: emb_idxs[i],
                 ..Default::default()