feat: add Database-Gateway Cloudron package (Infrastructure) [#639]

Database Gateway 0.24.0 as the 12th package: multi-stage Go build
(CGO required by the libpg_query parser, hence an alpine:3.23 runtime
matching upstream), native OIDC wired to the Cloudron platform identity
provider, postgresql addon storage with goose migrations applied at
start, jq-generated config + OPA policy seeded to /app/data. Verified
end-to-end against a throwaway postgres (migrations, policy compile,
startup to the OIDC handoff). Docs gardened to 12 packages.

Ticket: https://projects.knownelement.com/issues/639

Package-Workspace/Infrastructure/database-gateway/CloudronManifest.json

@@ -0,0 +1,24 @@
+{
+  "manifestVersion": 2,
+  "type": "app",
+  "id": "io.cloudron.dbgateway",
+  "title": "Database Gateway",
+  "description": "Web gateway for secure, policy-controlled access to PostgreSQL databases. Users authenticate via OIDC (Cloudron single sign-on) and run queries that are parsed and authorized by embedded OPA policies per user, target, operation and table. Query results are stored with shareable links for debugging and auditing.",
+  "author": "Kirill Zhuravlev",
+  "website": "https://github.com/kazhuravlev/database-gateway",
+  "contactEmail": "cloudron@tsys.dev",
+  "tagline": "Policy-checked SQL gateway for your databases",
+  "version": "0.24.0",
+  "healthCheckPath": "/",
+  "httpPort": 8080,
+  "memoryLimit": 512,
+  "addons": {
+    "localstorage": true,
+    "postgresql": {
+      "version": "16"
+    }
+  },
+  "mediaLinks": [],
+  "changelog": "Initial Cloudron package for Database Gateway 0.24.0. Native OIDC login wired to the Cloudron platform identity provider (admins group -> gateway admin, users group -> gateway user); local PostgreSQL addon stores profiles, bookmarks and query results; OPA policies and database targets are configured from /app/data. Single HTTP listener on port 8080.",
+  "icon": "file://logo.png"
+}