v0.4.0 — observability suite

A front-to-back observability release — seven new dashboard areas, each built to the same production-first posture as the rest of Vigilance (captured cheaply, flushed after the response, sampled and bounded). Full guide: docs/observability.md.

Added

• Unified Issues error tracker (/vigilance/issues) — every exception across web, queue, command, Vigilance::report() and browser errors, fingerprinted into a grouped inbox with stacktrace, context, occurrence sparkline and an assign / prioritise / ack / mute / resolve workflow.
• Per-route performance (/vigilance/routes) — throughput, error rate, Apdex and exact p50/p95/p99 latency per route.
• Real User Monitoring (/vigilance/vitals) — Core Web Vitals (LCP/INP/CLS/FCP/TTFB) + JS errors from real visitors via the @vigilanceRum beacon. Off by default (VIGILANCE_RUM).
• SLOs & error budgets (/vigilance/slos) — availability / latency objectives vs. an error budget, with a short-window burn-rate alert.
• Alerting depth & incidents (/vigilance/incidents) — Discord, Microsoft Teams and generic webhooks on top of mail / Slack; fired alerts persisted as incidents (auto-resolved) with occurrence counts and MTTR.
• Custom business metrics (/vigilance/custom-metrics) — Vigilance::increment() / gauge() → auto-discovered counter & gauge cards with sparklines.
• Trace-correlated log explorer (/vigilance/logs) — searchable application logs correlated to the trace that emitted them. Off by default (VIGILANCE_LOGS).

Changed

• Tracing now also records redis, mail and notification spans.
• New docs/observability.md; README + docs site updated. Every new page verified with axe-core — zero violations, desktop and mobile. CI on actions/checkout@v6.

Schema note: new columns/tables were folded into the base migration. If you ran a pre-0.4 dev build, run php artisan migrate:fresh to pick them up.