Rename project: battlenet-manager → umutray

Binary, crate, clap app name, ksni tray id, HTTP user-agent, systemd unit,
XDG config dir (co.aleshym/umutray), README, and all log prefixes.

Config path changes from ~/.config/battlenet-manager/ to ~/.config/umutray/.
Existing users should `mv` the old directory if they've customised it;
otherwise defaults get rewritten on next run.

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

src/config.rs

@@ -37,7 +37,7 @@ fn home_dir() -> PathBuf {
 
 impl Config {
     pub fn config_path() -> Result<PathBuf> {
-        let dirs = ProjectDirs::from("co.aleshym", "", "battlenet-manager")
+        let dirs = ProjectDirs::from("co.aleshym", "", "umutray")
             .context("Could not determine config directory")?;
         Ok(dirs.config_dir().join("config.toml"))
     }