Return SLO burn-down rate visualization data .

Provides:

• Current SLO compliance and error budget fraction
• Burn rate relative to the allowed failure rate (1.0 = on-target)
• Linear projection of days until the SLO is breached
• Sparkline data points for rendering a burn-down chart
• Human-readable breach projection summary

Example response::

{
  "slo_name": "task_success",
  "slo_target": 0.9,
  "slo_current": 0.942,
  "burn_rate": 0.3,
  "burn_rate_per_day": 0.05,
  "budget_fraction": 0.72,
  "budget_consumed_pct": 28.0,
  "days_to_breach": 6.1,
  "breach_projection": "SLO will breach in 6.1 days at current rate",
  "status": "green",
  "sparkline": [...]
}