feat: Add Grafana auto-update & improve classifier

Add auto-update for Grafana on Synology via SSH + docker compose,
with review examples and a context.txt describing the specific setup
(Prometheus + Node Exporter, no plugins) so the classifier can
ignore plugin-only breaking changes.

The classifier now loads an optional context.txt per service to
tailor decisions to the actual deployment. It also truncates large
release notes intelligently, keeping important sections (breaking
changes, deprecations, migration notes) while dropping long PR
lists that add no signal.

test_classifier.py now also loads context.txt and accepts any
service name as argument.

services/grafana/review-examples/auto-3.txt

@@ -0,0 +1,20 @@
+action: auto
+reason: The only breaking change is about plugin environment variables, which does not affect a simple Prometheus + Node Exporter setup with no third-party plugins installed.
+---
+[Download page](https://grafana.com/grafana/download/12.4.0)
+[What's new highlights](https://grafana.com/docs/grafana/latest/whatsnew/)
+
+### Breaking changes
+
+- **Plugins:** Prevent passing host environment variables to plugin processes by default
+
+### Features and enhancements
+
+- **Alerting:** Add Alert Rules tabs navigation with feature toggle
+- **Dashboards:** Add ability to share dashboards externally
+- **Plugins:** Forward AWS SDK credential chain env vars to external AWS plugins
+
+### Bug fixes
+
+- **Dashboards:** Fix panel rendering issue with long time ranges
+- **Prometheus:** Fix label matching in metric browser