Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/flex-objects/permissions.yaml

@@ -1,45 +0,0 @@
-actions:
-  admin.flex-objects:
-    type: crudl
-    label: Flex Objects
-
-types:
-  crudpl:
-    type: crud
-    use:
-      - crudp
-      - crudl
-
-  crudp:
-    type: crud
-    letters:
-      p:
-        action: publish
-        label: PLUGIN_ADMIN.PUBLISH
-
-  crudl:
-    type: crud
-    letters:
-      l:
-        action: list
-        label: PLUGIN_ADMIN.LIST
-
-  crud:
-    type: compact
-    letters:
-      c:
-        action: create
-        label: PLUGIN_ADMIN.CREATE
-      r:
-        action: read
-        label: PLUGIN_ADMIN.READ
-      u:
-        action: update
-        label: PLUGIN_ADMIN.UPDATE
-      d:
-        action: delete
-        label: PLUGIN_ADMIN.DELETE
-
-  default:
-    type: access
-