Conditional / scheduled boxes: show a box only when a rule fires

[dcondrey]

Let users configure a board where boxes appear based on rules or a schedule rather than always being present. Examples:

• Show the Traffic over time box only when traffic spikes above X or dips below Y vs the previous period.
• Show an Anomalies box only when there is an active anomaly.
• Time-of-day / day-of-week scheduling for which boxes are visible.

Sketch:

• Extend the persisted slot (lib/tiles.tsx Slot / lib/boardLayout.ts) with an optional rule (e.g. { metric, op, threshold } or a schedule window).
• Evaluate rules against the already-computed TileContext in BentoBoard and filter the rendered slots.
• Add a small rule editor in Customize mode.

Start with a single rule type (metric threshold vs previous period) end-to-end; the delta data is already fetched (KPI deltas are always-on).