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/main.rs

@@ -299,6 +299,16 @@ enum GraphCmd {
         /// Optional reason
         reason: Vec<String>,
     },
+    /// Set strength of an existing link
+    #[command(name = "link-set")]
+    LinkSet {
+        /// Source node key
+        source: String,
+        /// Target node key
+        target: String,
+        /// Strength (0.0–1.0)
+        strength: f32,
+    },
     /// Simulate adding an edge, report topology impact
     #[command(name = "link-impact")]
     LinkImpact {
@@ -775,6 +785,8 @@ fn main() {
             GraphCmd::Link { key } => cli::graph::cmd_link(&key),
             GraphCmd::LinkAdd { source, target, reason }
                 => cli::graph::cmd_link_add(&source, &target, &reason),
+            GraphCmd::LinkSet { source, target, strength }
+                => cli::graph::cmd_link_set(&source, &target, strength),
             GraphCmd::LinkImpact { source, target }
                 => cli::graph::cmd_link_impact(&source, &target),
             GraphCmd::LinkAudit { apply } => cli::graph::cmd_link_audit(apply),