feat(cli): add 'lore related' semantic similarity command (bd-8con)

Adds 'lore related' / 'lore similar' command for discovering semantically
related issues and MRs using vector embeddings.

Two modes:
- Entity mode: find entities similar to a specific issue/MR
- Query mode: embed free text and find matching entities

Includes distance-to-similarity conversion, label intersection,
human and robot output formatters, and 11 unit tests.

.beads/last-touched

@@ -1 +1 @@
-bd-2o49
+bd-8con