Declare plugin settings in the manifest, resolve them from the environment

compose.override.yml

@@ -22,7 +22,7 @@ services:
       PLUGIN_DB_URL: *plugin-db-url
       REQUIRE_SECURE_SECRETS: "false"
       SECURE_COOKIES: "false" # dev serves http — Secure cookies wouldn't be sent
-      SCHEDULING_UPSTREAM: "http://shifts-upstream:4000" # backs the reference plugin once you copy it into plugins/
+      PLUGIN_SETTING_SCHEDULING_UPSTREAM: "http://shifts-upstream:4000" # backs the reference plugin once you copy it into plugins/
     volumes:
       - .:/app
       # Mount your own menu/branding override into the empty config/ dir (defaults apply otherwise):
@@ -46,8 +46,8 @@ services:
 
   # Mock backend ready for the reference plugin (examples/plugins/scheduling): plugins/ ships empty, so
   # the plugin is opt-in — `cp -r examples/plugins/scheduling plugins/scheduling`, restart, and this
-  # backs it (SCHEDULING_UPSTREAM above points here). Stand-in for the customer's real service —
-  # stdlib-only, in-memory, no auth. Prod points SCHEDULING_UPSTREAM at the real backend instead.
+  # backs it (PLUGIN_SETTING_SCHEDULING_UPSTREAM above points here). Stand-in for the customer's real service —
+  # stdlib-only, in-memory, no auth. Prod points PLUGIN_SETTING_SCHEDULING_UPSTREAM at the real backend instead.
   shifts-upstream:
     image: node:24.19.0-alpine3.24
     command: node /srv/server.ts