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

Cargo.toml

@@ -0,0 +1,49 @@
+[package]
+name = "claude-code-usage-bubble"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0"
+description = "Floating bubble showing Claude Code and Codex usage on Windows"
+homepage = "https://github.com/tiennm99/claude-code-usage-bubble"
+repository = "https://github.com/tiennm99/claude-code-usage-bubble"
+
+[package.metadata.winres]
+ProductName = "Claude Code Usage Bubble"
+FileDescription = "Claude Code Usage Bubble"
+OriginalFilename = "claude-code-usage-bubble.exe"
+InternalName = "ClaudeCodeUsageBubble"
+LegalCopyright = "Copyright (C) 2026"
+Comments = "Floating bubble showing Claude Code and Codex usage on Windows"
+
+[dependencies]
+ureq = { version = "2", default-features = false, features = ["native-tls", "json", "proxy-from-env"] }
+native-tls = "0.2"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+dirs = "6"
+
+[dependencies.windows]
+version = "0.58"
+features = [
+    "Win32_Foundation",
+    "Win32_Globalization",
+    "Win32_Graphics_Gdi",
+    "Win32_System_LibraryLoader",
+    "Win32_UI_Shell",
+    "Win32_UI_WindowsAndMessaging",
+    "Win32_System_Registry",
+    "Win32_System_Threading",
+    "Win32_Security",
+    "Win32_UI_HiDpi",
+    "Win32_UI_Input_KeyboardAndMouse",
+]
+
+[build-dependencies]
+winres = "0.1"
+
+[profile.release]
+opt-level = "z"
+lto = true
+strip = true
+codegen-units = 1
+panic = "abort"