design at /slo
## What
Adds **SLO burn-rate alerts** — an alert family that fires off an SLO's
error budget rather than a raw query — and finishes the SLO surface
around it: navigation entry, detail-page fixes, and the flag removal now
that SLOs have shipped.
## Changes
**SLO burn-rate alerts (backend)**
- New burn-rate evaluation (`config/src/meta/slo/burn.rs`,
`condition.rs`) with multi-window burn conditions, and
`core/src/slo/evaluate.rs` extended to evaluate them on the SLO job.
- Alerts carry an `slo_id`; `infra/src/table/alerts` gains the column,
filtering, and query support so an SLO's alerts can be listed and
deleted with it.
- Alert levels (`meta/alerts/level.rs`) and tags extended for the SLO
family; scheduler handlers route SLO alerts through the same
notification path.
**SLO alert UI**
- `SloAlertForm` + `AlertDetailSlo`: create, edit and view burn-rate
alerts from the SLO detail page and the alert list.
- Payload/routing helpers (`utils/alerts/sloAlertPayload.ts`,
`sloAlertRouting.ts`, `alertPayload.ts`) with unit tests.
- `AlertDestinationsField` extracted as the complete Destination form
field — side label, tooltip, combined destinations/workflows picker,
inline error, refresh, and create-in-new-tab. It replaces two verbatim
copies in the generic alert form and is reused by the SLO form and
synthetics `CheckAlerts` (which sets `supportsWorkflows: false`, since a
check has no workflow routing). Fixes the SLO form's previously unwired
refresh and Add Destination buttons.
**SLO detail page fixes**
- Burndown and burn-rate charts drew as bare axes when coverage was
sparse: `showSymbol: false` means an isolated measured bucket between
gaps has no segment and paints nothing. Symbols are now sized per point,
and a sparse-coverage note states how many buckets actually recorded
events.
- Nothing scrolled below ~700px of viewport height — `OPageLayout`'s
fixed flex body plus `OTabPanels` `scroll="none"` clipped the panels.
Panels now grow and scroll; the stat strip and tab bar stay pinned.
Verified at 1024x500, 1280x620, 1512x945.
**Other**
- `ZO_SLO_ENABLED` removed — SLOs have shipped, so the flag and its
status/route gating are gone.
- SLOs surfaced in the main nav.
- Dashboard chart panel header gets its own tint via new
`--color-panel-bar-bg` / `--color-panel-bar-border` tokens, and the bar
is extracted into `PanelBar.vue` (it existed as five hand-copied class
strings that had already drifted).
- `tsconfig.vitest.tsbuildinfo` untracked; third-party vendor name
removed from comments and test names.
## Testing
- New Rust tests across `meta/slo/burn.rs`, `condition.rs`,
`core/src/alerts/alert.rs` and `infra/src/table/alerts`.
- New frontend suites: `sloAlertPayload.spec.ts`,
`sloAlertRouting.spec.ts`, `alertPayload.spec.ts`,
`AlertDetailSlo.spec.ts`, `SloDetailAlerts.spec.ts`,
`SloListDelete.spec.ts`, `SloTimeSlicePreview.spec.ts`.
- `cargo clippy --all-targets` and `web` `lint:ci` clean.
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