feat(prometheus-direct-charting): slice 3 — remove grafana + config rewrite + changelog

Remove the entire Grafana surface: integrations/grafana.py, GrafanaWidgetSource
(+ _fetch_chart, now redundant since prometheus chart exists), GrafanaLinkWidget,
LinksTab, get_grafana_status endpoint, useGrafanaStatus hook, GrafanaStatus type,
fetchGrafanaStatus client fn, registry/nav/tab entries (FE+BE). Rewrite
config.yaml thin-dashboard rule to match reality (recharts is sanctioned for
Prometheus-backed series). CHANGELOG migration note added.

Backend: 293 pytest pass, ruff clean. Frontend: build+lint green (0 errors).
SC-115/116 grep-clean (only prometheus_range.py migration comments + Dashboard.test
shortcut fixture remain — both spec-allowed).

CHANGELOG.md

@@ -4,6 +4,24 @@ All notable changes to Manage. Breaking changes are marked with **BREAKING**.
 
 ## [Unreleased]
 
+### Added — Direct Prometheus charting
+
+- **Prometheus is now the direct source for in-app charts.** New widget kinds
+  on the `prometheus` service: `chart` (multi-series line chart via recharts,
+  backed by `/api/v1/query_range`), `gauge` (instant scalar with configurable
+  threshold bands), and `mean` (client-side average over a time window).
+
+### **BREAKING** — Grafana service type removed
+
+- The `grafana` service type, Grafana link widget, Grafana chart widget, and
+  `GET /api/monitoring/grafana-status` endpoint were **removed**. Manage now
+  queries Prometheus directly for all chart data.
+- **Migration:** Delete any existing Grafana service instances and create
+  Prometheus service instances instead (pointing at your Prometheus URL). Any
+  configured `grafana/chart` widgets must be recreated as `prometheus/chart`
+  widgets. Grafana link widgets are gone — use Prometheus chart/metric widgets
+  instead.
+
 ### Added — Observability service registry
 
 - **Alertmanager is now a service type.** Configure Alertmanager, Grafana, and