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/migrate.rs

@@ -23,19 +23,10 @@ use std::collections::HashMap;
 use std::env;
 use std::fs;
 use std::path::{Path, PathBuf};
-use std::time::{SystemTime, UNIX_EPOCH};
-
 fn home() -> PathBuf {
     PathBuf::from(env::var("HOME").expect("HOME not set"))
 }
 
-fn now_epoch() -> f64 {
-    SystemTime::now()
-        .duration_since(UNIX_EPOCH)
-        .unwrap()
-        .as_secs_f64()
-}
-
 // Old system data structures (just enough for deserialization)
 
 #[derive(Deserialize)]
@@ -206,7 +197,7 @@ pub fn migrate() -> Result<(), String> {
         let node = Node {
             uuid,
             version: 1,
-            timestamp: now_epoch(),
+            timestamp: capnp_store::now_epoch(),
             node_type: if key.contains("journal") {
                 NodeType::EpisodicSession
             } else {
@@ -246,7 +237,7 @@ pub fn migrate() -> Result<(), String> {
         let node = Node {
             uuid,
             version: 1,
-            timestamp: now_epoch(),
+            timestamp: capnp_store::now_epoch(),
             node_type: if key.contains("journal") {
                 NodeType::EpisodicSession
             } else {