query: rich QueryResult + toolkit cleanup

QueryResult carries a fields map (BTreeMap<String, Value>) so callers
don't re-resolve fields after queries run. Neighbors queries inject
edge context (strength, rel_type) at construction time.

New public API:
- run_query(): parse + execute + format in one call
- format_value(): format a Value for display
- execute_parsed(): internal, avoids double-parse in run_query

Removed: output_stages(), format_field()

Simplified commands:
- cmd_query, cmd_graph, cmd_link, cmd_list_keys all delegate to run_query
- cmd_experience_mine uses existing find_current_transcript()

Deduplication:
- now_epoch() 3 copies → 1 (capnp_store's public fn)
- hub_threshold → Graph::hub_threshold() method
- eval_node + eval_edge → single eval() with closure for field resolution
- compare() collapsed via Ordering (35 → 15 lines)

Modernization:
- 12 sites of partial_cmp().unwrap_or(Ordering::Equal) → total_cmp()

src/similarity.rs

@@ -100,7 +100,7 @@ pub fn pairwise_similar(
         }
     }
 
-    results.sort_by(|a, b| b.2.partial_cmp(&a.2).unwrap_or(std::cmp::Ordering::Equal));
+    results.sort_by(|a, b| b.2.total_cmp(&a.2));
     results
 }