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-2.txt

@@ -0,0 +1,18 @@
+action: auto
+reason: Security-only patch release. No breaking changes, no configuration changes, no manual steps required.
+---
+[Download page](https://grafana.com/grafana/download/12.3.6)
+[What's new highlights](https://grafana.com/docs/grafana/latest/whatsnew/)
+
+### Features and enhancements
+
+- **Public Dashboards:** Prevent unintended CRUD operations from different orgs
+
+### Bug fixes
+
+- **Security:** Fixes CVE-2026-27876
+- **Security:** Fixes CVE-2026-27877
+- **Security:** Fixes CVE-2026-28375
+- **Security:** Fixes CVE-2026-27879
+- **Security:** Fixes CVE-2026-27880
+- **Security:** Fixes CVE-2026-27876