chore: satisfy CI fmt/clippy gates; make the release publish step idempotent

`cargo fmt --all -- --check` and `cargo clippy --all-targets -- -D warnings` are
CI gates and both were failing on this release's code.

- rustfmt across the files touched by the release
- `.split('/').last()` walks the whole iterator on a DoubleEndedIterator; use
  `.next_back()` (4 sites in the setup/featured + delete handlers)
- `set_progress` had two identical branches; the intent is "take the first
  reading, then only move forward", which is one condition

release.yml published unconditionally on a version tag, so a version already on
crates.io (released by hand, or a re-run of the job) failed the workflow — a
version can never be re-uploaded. It now checks the registry and skips instead.

src/config.rs

@@ -774,7 +774,10 @@ pub fn default_config_path() -> String {
     if std::path::Path::new("Cargo.toml").exists() && std::path::Path::new("config").exists() {
         return repo_path.to_string();
     }
-    data_dir().join("gateway.toml").to_string_lossy().into_owned()
+    data_dir()
+        .join("gateway.toml")
+        .to_string_lossy()
+        .into_owned()
 }
 
 impl Config {