feat: wire KPI telemetry — web-vitals RUM + missing events + POST sink

[OmarEhab007]

Problem

The telemetry system fires DOM events locally but has no production sink. Two PRD KPI events are defined but never fired:

• `core_workflow_complete` — defined in types, never dispatched
• `time_to_first_insight_seconds` — not even defined yet

Without these, the PRD success metrics (adoption rate, time-to-insight, usability score) cannot be measured.

Scope

1. Add `web-vitals` package — report LCP, INP, CLS via `trackEvent`
2. Add `time_to_first_insight_seconds` event — measure from `dashboard_render_complete` to first detail navigation
3. Fire `core_workflow_complete` in the log explorer on workflow completion
4. Extend `trackEvent` to POST to `NEXT_PUBLIC_TELEMETRY_URL` when set (no-op if unset)
5. Tests for all new telemetry paths

Acceptance Criteria

• `web-vitals` installed; LCP/INP/CLS reported via `trackEvent` on every page
• `time_to_first_insight_seconds` fires when user reaches first detail view from dashboard
• `core_workflow_complete` fires in log explorer on workflow completion
• `trackEvent` POSTs to `NEXT_PUBLIC_TELEMETRY_URL` when env var is set
• All new paths have Vitest tests
• 0 lint errors, 0 tsc errors

References

PRD KPIs: `projects/RemedyIQ/prd-ui-refactor-core-focus.md`
Audit gap: `projects/RemedyIQ/audit-refactor-scoping-q1.md` — "No RUM"