Rename the CLI package to tsunagi and its executable to tsng

The command line package is now `tsunagi` and builds the `tsng` executable,
which the packages, the unit, the installers and the workflows install and
run. The core library package becomes `tsunagi-core`, keeping the library name
`tsunagi`, so no code changes `use tsunagi::...`. Directories follow
(crates/tsunagi-core, crates/tsunagi). Every command shown to a person is now
`tsng ...`.

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

docs/routing.md

@@ -75,7 +75,7 @@ neither administrative rights nor public relays/DHT.
 Run the forwarding microbenchmark explicitly:
 
 ```sh
-cargo test --release -p tsunagi --lib forwarding_benchmark -- --ignored --nocapture
+cargo test --release -p tsunagi-core --lib forwarding_benchmark -- --ignored --nocapture
 ```
 
 It processes one million 64-byte frames and one million 1280-byte frames with