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/commands/mod.rs

@@ -1,6 +1,7 @@
 pub mod auth_test;
 pub mod count;
 pub mod doctor;
+pub mod drift;
 pub mod embed;
 pub mod generate_docs;
 pub mod ingest;
@@ -20,6 +21,7 @@ pub use count::{
     run_count_events,
 };
 pub use doctor::{DoctorChecks, print_doctor_results, run_doctor};
+pub use drift::{DriftResponse, print_drift_human, print_drift_json, run_drift};
 pub use embed::{print_embed, print_embed_json, run_embed};
 pub use generate_docs::{print_generate_docs, print_generate_docs_json, run_generate_docs};
 pub use ingest::{