Add calibrate agent, link-set command, and dominating-set query stage

calibrate.agent: Haiku-based agent that reads a node and all its
neighbors, then assigns appropriate link strengths relative to each
other. Designed for high-volume runs across the whole graph.

graph link-set: Set strength of an existing link (0.0-1.0).

dominating-set query stage: Greedy 3-covering dominating set — finds
the minimum set of nodes such that every node in the input is within
1 hop of at least 3 selected nodes. Use with calibrate agent to
ensure every link gets assessed from multiple perspectives.

Usage: poc-memory query "content ~ 'bcachefs' | dominating-set"

poc-memory/src/query/parser.rs

@@ -64,6 +64,7 @@ pub enum Stage {
     Select(Vec<String>),
     Count,
     Connectivity,
+    DominatingSet,
 }
 
 #[derive(Debug, Clone)]
@@ -90,6 +91,7 @@ peg::parser! {
             / "select" _ f:field_list() { Stage::Select(f) }
             / "count" { Stage::Count }
             / "connectivity" { Stage::Connectivity }
+            / "dominating-set" { Stage::DominatingSet }
 
         rule asc_desc() -> bool
             = "asc" { true }
@@ -425,6 +427,15 @@ fn execute_parsed(
             }
             Stage::Connectivity => {} // handled in output
             Stage::Select(_) | Stage::Count => {} // handled in output
+            Stage::DominatingSet => {
+                let mut items: Vec<(String, f64)> = results.iter()
+                    .map(|r| (r.key.clone(), graph.degree(&r.key) as f64))
+                    .collect();
+                let xform = super::engine::Transform::DominatingSet;
+                items = super::engine::run_transform(&xform, items, store, &graph);
+                let keep: std::collections::HashSet<String> = items.into_iter().map(|(k, _)| k).collect();
+                results.retain(|r| keep.contains(&r.key));
+            }
         }
     }