Add PocketBase schema migrations and migration pipeline

- 8 collections: vereine, gruppen, mitglieder, beitraege, einzuege,
  termine, nachrichten, push_subscriptions
- verein_id relation added to users (multi-tenant isolation)
- API rules enforce tenant separation via @request.auth.verein_id
- docker-compose: --migrationsDir=/pb_data/migrations flag + volume mount
- Makefile: migrations sync step added to deploy target

pocketbase/pb_migrations/1779215948_created_push_subscriptions.js

@@ -0,0 +1,94 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((app) => {
+  const collection = new Collection({
+    "createRule": "@request.auth.id != ''",
+    "deleteRule": "@request.auth.id = user_id",
+    "fields": [
+      {
+        "autogeneratePattern": "[a-z0-9]{15}",
+        "help": "",
+        "hidden": false,
+        "id": "text3208210256",
+        "max": 15,
+        "min": 15,
+        "name": "id",
+        "pattern": "^[a-z0-9]+$",
+        "presentable": false,
+        "primaryKey": true,
+        "required": true,
+        "system": true,
+        "type": "text"
+      },
+      {
+        "cascadeDelete": true,
+        "collectionId": "_pb_users_auth_",
+        "help": "",
+        "hidden": false,
+        "id": "relation2809058197",
+        "maxSelect": 1,
+        "minSelect": 0,
+        "name": "user_id",
+        "presentable": false,
+        "required": true,
+        "system": false,
+        "type": "relation"
+      },
+      {
+        "exceptDomains": null,
+        "help": "",
+        "hidden": false,
+        "id": "url3292663675",
+        "name": "endpoint",
+        "onlyDomains": null,
+        "presentable": false,
+        "required": true,
+        "system": false,
+        "type": "url"
+      },
+      {
+        "autogeneratePattern": "",
+        "help": "",
+        "hidden": false,
+        "id": "text3303707132",
+        "max": 0,
+        "min": 0,
+        "name": "p256dh",
+        "pattern": "",
+        "presentable": false,
+        "primaryKey": false,
+        "required": true,
+        "system": false,
+        "type": "text"
+      },
+      {
+        "autogeneratePattern": "",
+        "help": "",
+        "hidden": false,
+        "id": "text4175343705",
+        "max": 0,
+        "min": 0,
+        "name": "auth",
+        "pattern": "",
+        "presentable": false,
+        "primaryKey": false,
+        "required": true,
+        "system": false,
+        "type": "text"
+      }
+    ],
+    "id": "pbc_1438754935",
+    "indexes": [],
+    "listRule": "@request.auth.id = user_id",
+    "name": "push_subscriptions",
+    "system": false,
+    "type": "base",
+    "updateRule": "@request.auth.id = user_id",
+    "viewRule": "@request.auth.id = user_id"
+  });
+
+  return app.save(collection);
+}, (app) => {
+  const collection = app.findCollectionByNameOrId("pbc_1438754935");
+
+  return app.delete(collection);
+})