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/main.rs

@@ -14,7 +14,7 @@ use std::path::PathBuf;
 /// Running without a subcommand starts the system tray daemon.
 /// Use `launch` in your .desktop shortcut for a direct, no-UI launch.
 #[derive(Parser)]
-#[command(name = "battlenet-manager", version, about)]
+#[command(name = "umutray", version, about)]
 struct Cli {
     #[command(subcommand)]
     command: Option<Commands>,