v0.2.16 — Claude Code support

Adds Claude Code account management alongside Codex: OAuth login (paste-code flow), .credentials.json/Keychain import, API key accounts, real usage-window data from Anthropic's OAuth usage API, warm-up, and safe account switching that blocks while the claude CLI is running. Codex and Claude accounts can now be active independently at the same time, with a tabbed UI and menu bar/tray support for both.

macOS Apple Silicon: current release builds are not Apple-notarized. If macOS says the app is damaged, move it to /Applications and remove the quarantine flag:
```bash
sudo xattr -dr com.apple.quarantine "/Applications/Codex Switcher.app"
open "/Applications/Codex Switcher.app"
```