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/service.rs

@@ -2,7 +2,7 @@ use anyhow::{bail, Context, Result};
 use std::path::PathBuf;
 use std::process::Command;
 
-const UNIT_NAME: &str = "battlenet-manager.service";
+const UNIT_NAME: &str = "umutray.service";
 
 fn unit_path() -> Result<PathBuf> {
     let home = std::env::var("HOME").context("$HOME is not set")?;