Pace tick, ETA & burn-rate alerts

[ashalliants]

What this adds

Turns the widget from a passive percentage display into something that tells you whether you're burning quota too fast — all derived from data already shown (percentage used + reset time + the known window length).

• Pace tick on each Claude bar marking where usage should be given how far through the window you are. Fill ahead of the tick = pacing to run out early.
• Pace-based colour on the % text (green/amber/red) in single-provider mode; multi-provider keeps the existing per-provider tint, with the tick carrying the pace signal.
• Richer per-provider tray tooltip: exact local reset time (e.g. resets 4:45 PM), multi-unit countdown (2h 15m), and ~1h20m left at this rate when over pace.
• Burn-rate alerts (opt-in, default Off): a balloon + danger badge (brief flash then steady) when pacing to run out. New Usage alerts submenu with presets: Off / At 90% / At 80% & 90% / Pacing to run out. Persisted to settings.

Design notes

• All pace/ETA/alert maths live in a new pure, unit-tested src/pace.rs module.
• Pace UI is shown only where the window length is reliably known (Claude session = 5h, weekly = 7d). Codex/Antigravity return None and are gracefully omitted — never a fabricated signal.
• Alerts are edge-triggered (fire once on entering the state, re-arm after it clears/resets), mirroring the existing auth-balloon gate.
• New user-facing strings added to all 11 locales (English values as fallback pending translation).

Verification

Builds clean and cargo test passes on Windows (MSVC). Not yet runtime/visually verified — a quick cargo run smoke-test of the tick/colour/tooltip/alert is recommended.