test: persistence e2e and registration-relogin e2e; lint clean

Adds a lib target (soulseek_rs_tui) exposing cli/models/persist so
integration tests can drive the persistence pipeline: state and config
survive a simulated restart through the real files, with the incomplete
download flagged for auto-resume. The lib e2e suite gains a
register-then-relogin test against soulfind proving the stored-credential
flow's server assumptions. cargo clippy --all-targets and cargo fmt are
clean.

soulseek-rs/Cargo.toml

@@ -13,6 +13,13 @@ categories = ["command-line-utilities"]
 name = "soulseek-rs"
 path = "src/main.rs"
 
+# Small library target so integration tests can exercise the persistence
+# pipeline; the dependency soulseek-rs-lib already owns the `soulseek_rs`
+# crate name, hence the distinct one.
+[lib]
+name = "soulseek_rs_tui"
+path = "src/lib.rs"
+
 [lints]
 workspace = true