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/graph.rs

@@ -73,6 +73,19 @@ impl Graph {
         &self.communities
     }
 
+    /// Hub degree threshold: top 5% by degree
+    pub fn hub_threshold(&self) -> usize {
+        let mut degrees: Vec<usize> = self.keys.iter()
+            .map(|k| self.degree(k))
+            .collect();
+        degrees.sort_unstable();
+        if degrees.len() >= 20 {
+            degrees[degrees.len() * 95 / 100]
+        } else {
+            usize::MAX
+        }
+    }
+
     /// Local clustering coefficient: fraction of a node's neighbors
     /// that are also neighbors of each other.
     /// cc(v) = 2E / (deg * (deg - 1))
@@ -187,7 +200,7 @@ impl Graph {
         let n = degrees.len();
         if n < 2 { return 0.0; }
 
-        degrees.sort_by(|a, b| a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal));
+        degrees.sort_by(|a, b| a.total_cmp(b));
         let mean = degrees.iter().sum::<f64>() / n as f64;
         if mean < 1e-10 { return 0.0; }
 
@@ -255,17 +268,7 @@ impl Graph {
     pub fn link_impact(&self, source: &str, target: &str) -> LinkImpact {
         let source_deg = self.degree(source);
         let target_deg = self.degree(target);
-
-        // Hub threshold: top 5% by degree
-        let mut all_degrees: Vec<usize> = self.keys.iter()
-            .map(|k| self.degree(k))
-            .collect();
-        all_degrees.sort_unstable();
-        let hub_threshold = if all_degrees.len() >= 20 {
-            all_degrees[all_degrees.len() * 95 / 100]
-        } else {
-            usize::MAX // can't define hubs with <20 nodes
-        };
+        let hub_threshold = self.hub_threshold();
         let is_hub_link = source_deg >= hub_threshold || target_deg >= hub_threshold;
 
         // Community check
@@ -469,7 +472,7 @@ fn label_propagation(
 
             // Adopt the label with most votes
             if let Some((&best_label, _)) = votes.iter()
-                .max_by(|a, b| a.1.partial_cmp(b.1).unwrap_or(std::cmp::Ordering::Equal))
+                .max_by(|a, b| a.1.total_cmp(b.1))
             {
                 let current = labels[key];
                 if best_label != current {