init: archlens — architecture diagram generator

Hex arch + DDD, tree-sitter parsing, Mermaid/ASCII output.
Supports Rust + Python. 92 tests. CI, diff, --check for staleness detection.

crates/adapters/walkdir/src/lib.rs

@@ -0,0 +1,3 @@
+mod walkdir_discovery;
+
+pub use walkdir_discovery::WalkdirDiscovery;