feat: vault walker with incremental diff detection and .gitignore support

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: devwhodevs

Cargo.lock

@@ -22,6 +22,8 @@ ureq = "2.12"
 indicatif = "0.17"
 ndarray = "0.17"
 hnsw_rs = "0.3"
+rayon = "1"
+ignore = "0.4"
 
 [dev-dependencies]
 tempfile = "3"