feat: add weekly on-pace usage budgets

[simon-ami]

Summary

• Show weekly usage budgets for now, one hour, five hours, and today.
• Add an expandable weekly pace chart with ideal, average, and projected usage.
• Keep session windows unchanged.
• Preserve the reserve fallback when timing data is incomplete.

Closes #86

Testing

• Frontend tests passed: 89 tests.
• Production frontend build passed.
• Manually tested using the portable Windows executable.

Preview

Default:

Expanded:

[simon-ami]

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[Finesssee]

Thermo-nuclear review found two changes needed before this is merge-ready:

1. MenuCard.tsx currently fabricates reserve status with snap.reserveDescription ?? "Lasts until reset". That status is backend-owned and should only appear when the bridge/backend pace analysis provides it. Please omit the secondary status when reserveDescription is missing, or move this into a small view-model helper that preserves the backend contract.

2. The fallback reserve row is now gated by the weekly-window check. That hides valid backend-provided reservePercent / reserveDescription whenever timing metadata is incomplete. Explicit reserve metadata should render independently of whether the frontend can compute the new budget pills. The fallback should be closer to:

snap.reservePercent != null && !paceBudget && !snap.isExhausted

Suggested cleanup: extract a small getMetricPaceView(snap) / PaceBudgetSection boundary that returns exactly one of: computed budget, explicit reserve row, or nothing. That keeps backend reserve semantics intact and removes the competing ad-hoc conditions from MetricRow.

[Finesssee]

Thanks for adding the weekly on-pace usage budgets and for preserving the backend pace metadata semantics after review — merged.