feat(bd-1cjx): add lore drift command for discussion divergence detection

Implement drift detection using cosine similarity between issue description
embedding and chronological note embeddings. Sliding window (size 3) identifies
topic drift points. Includes human and robot output formatters.

New files: drift.rs, similarity.rs
Closes: bd-1cjx

src/cli/mod.rs

@@ -215,6 +215,24 @@ pub enum Commands {
     /// People intelligence: experts, workload, active discussions, overlap
     Who(WhoArgs),
 
+    /// Detect discussion divergence from original intent
+    Drift {
+        /// Entity type (currently only "issues" supported)
+        #[arg(value_parser = ["issues"])]
+        entity_type: String,
+
+        /// Entity IID
+        iid: i64,
+
+        /// Similarity threshold for drift detection (0.0-1.0)
+        #[arg(long, default_value = "0.4")]
+        threshold: f32,
+
+        /// Scope to project (fuzzy match)
+        #[arg(short, long)]
+        project: Option<String>,
+    },
+
     #[command(hide = true)]
     List {
         #[arg(value_parser = ["issues", "mrs"])]