feat: initial port of claude-code-usage-monitor as a floating bubble

Windows-only floating, draggable circular bubble showing Claude Code
and Codex usage. Derivative of CodeZeno/Claude-Code-Usage-Monitor (MIT),
relicensed under Apache 2.0 with upstream attribution in NOTICE.

- Ported verbatim: poller, updater, tray_icon, theme, localization,
  diagnose, models (~2,700 LOC)
- Original: bubble (circular layered window, drag-anywhere via
  WM_NCHITTEST+HTCAPTION, snap-to-edge, Ctrl+Wheel resize, auto-hide
  on fullscreen), panel (expanded 5h/7d view), app (orchestrator,
  single-instance mutex, polling thread, context menu, dual-bubble
  lifecycle), settings (settings.json persistence)
- Cargo.toml features cover Win32 GDI, HiDpi, Registry, Threading,
  Shell, WindowsAndMessaging, and KeyboardAndMouse

src/main.rs

@@ -0,0 +1,39 @@
+#![windows_subsystem = "windows"]
+
+mod app;
+mod bubble;
+mod diagnose;
+mod localization;
+mod models;
+mod native_interop;
+mod panel;
+mod poller;
+mod settings;
+mod theme;
+mod tray_icon;
+mod updater;
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    let diagnose_enabled = args.iter().any(|a| a == "--diagnose");
+    if diagnose_enabled {
+        if let Ok(path) = diagnose::init() {
+            diagnose::log(format!(
+                "startup args={args:?} log_path={}",
+                path.display()
+            ));
+        }
+    }
+
+    if let Some(exit_code) = updater::handle_cli_mode(&args) {
+        if diagnose_enabled {
+            diagnose::log(format!("cli mode exited with code {exit_code}"));
+        }
+        std::process::exit(exit_code);
+    }
+
+    if diagnose_enabled {
+        diagnose::log("entering app::run");
+    }
+    app::run();
+}