Remove Rust code, delegate server to nuwiki-rs repo

Delete all Rust crates (crates/) and Cargo files. The nuwiki-ls binary
is now built in the separate nuwiki-rs repository and downloaded at
install time from the Gitea release assets, with a cargo build fallback
that clones nuwiki-rs.

Update all documentation to reflect the split repo layout.

.gitignore

@@ -1,9 +1,10 @@
 # Rust build artifacts
 /target
-**/*.rs.bk
 
-# Plugin runtime: downloaded LSP binary lives here (see SPEC.md §7.2)
+# Plugin runtime: downloaded LSP binary lives here (see development/SPEC.md)
 /bin
+# nuwiki-rs is cloned here during install fallback, not tracked
+nuwiki-rs/
 
 # Editor / OS noise
 .DS_Store