feat: add GoAlert Cloudron package (Monitoring) [#633]

Official-image wrapper of goalert/goalert 0.34.1 (digest-pinned),
single Go binary + postgresql only. Native generic OIDC wired from
the platform provider (GOALERT_OIDC_*), data-encryption key
persisted, optional first-admin basic auth. grind-stack verified:
full migration chain, serving, origin canonicalization correct.
18th package; category table reconciled to the 46-app set.

Package-Workspace/Monitoring/goalert/CHANGELOG.md

@@ -0,0 +1,12 @@
+# Changelog — GoAlert Cloudron Package
+
+## 1.0.0 — 2026-09-06
+
+- Initial package: GoAlert 0.34.1 (official-image wrapper, digest-pinned
+  sha256:36b3962e…)
+- postgresql + localstorage addons; web/API on :8081; bash added for the
+  addon wait loop
+- GOALERT_DB_URL/PUBLIC_URL mapped from the platform env; data-encryption
+  key persisted under /app/data
+- Native OIDC wired from the platform provider, new-user creation on;
+  optional first-admin basic auth via GOALERT_ADMIN_USER/PASS env vars