Visualize durability trends to spot slow degradations

[timfong888]

User Story

When I review network health weekly,
I want to see 2-copy durability as a rolling 7-day and 30-day trend alongside the outcome distribution,
so I can spot slow-creeping problems that would not trip an alert but are drifting in the wrong direction.

Context

The trend window smooths out single incidents to reveal patterns. This is the view used for weekly prep, internal readouts, and catching "things are quietly getting worse" problems.

Acceptance Criteria

• 7-day and 30-day rolling 2-copy durability displayed as a line or area chart
• Stacked area chart showing 2-copy / 1-copy / 0-copy distribution over the same window
• WoW delta surfaced next to the current number
• Chart is drillable to a shorter window (e.g., click a day to see hourly)
• Low-volume handling per the windows Feature

Parent

• [UPLOAD-1] [UPLOAD-1] Know whether uploads are actually achieving 2-copy durability #1