[Feature] Flip the whole dashboard into a live realtime view (PULSE-17)

[uz1mani]

The dashboard's "current visitors" chip opens a popover and touches nothing else. Rebuild it so clicking it — or picking a new Realtime entry in the view switcher — flips the whole dashboard into a live view: headline stats, chart, and every block below, updating in realtime behind an orange pulsating orb.

Plane work item: https://plane-sks.ciphera.net/ciphera/projects/7f1d6ca7-7bcb-4af3-ba59-b5051602efa1/issues/47a0c7e4-e7fa-432f-805c-04fe735b2feb (PULSE-17)
Design doc: Pulse/docs/plans/22-09-2026-realtime-dashboard-mode-design.md

Frontend scope

• Realtime mode as a page-scoped extraPresets group + rollingMinutes, addressable as ?period=realtime. Copy the Visitors page precedent (lib/visitors/range.ts) rather than widening the shared Period grammar into every other page's picker.
• useRealtimeSync(siteId) — the single transport seam: ticket mint, WebSocket connect, exponential-backoff reconnect, visibility gating, 1s debounce, mutate() of the realtime keys, 5s poll fallback.
• Replace RealtimeVisitorsPopover's green animate-pulse chip with the orange orb (reuse the established two-span dot recipe, recoloured to brand-orange; count in tabular-nums, never font-mono).
• Feed CommandDeck a rolling last-30-min interval='minute' series; honour missingAsZero with the honest em-dash tooltip.
• Live top-N for Sources / Locations / TechSpecs / Outbound / ContentStats. PeakHours is hidden in realtime mode — a weekly hour-of-day heatmap has no meaning at a live instant.
• Same flip on components/share/PublicDashboard.tsx (owner decision: both surfaces), gated on the backend privacy pass.
• Preserve or deliberately repoint data-tour="realtime-trigger"; lib/tour/steps.ts anchors a step to it and will break silently otherwise.
• Resolve the dead lastUpdatedAt/1s-tick plumbing in PublicDashboard (computed, never rendered).

Constraints

• The whole-site live count is unfloored by explicit owner design — do not add an n>=5 floor to it.
• Facet is dark-only; all radii are 0 except full; brand-orange is #FD5E0F.
• animate-ping is unused in this codebase today — probe it against the shipped CSS in the mock round like any other class.
• A mocked-on-production options round is approved before any pixels are built.