Add rebuild tool: scan nginx volumes to reconstruct SQLite index

Walks nginx autoindex JSON recursively, merges replicas across volumes,
and bulk-inserts into a fresh database. Also adds reqwest json feature.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib.rs

@@ -4,6 +4,7 @@ pub mod error;
 pub mod hasher;
 pub mod health;
 pub mod server;
+pub mod rebuild;
 pub mod volume;
 
 use std::collections::HashSet;