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/1779215901_created_beitraege.js

@@ -0,0 +1,97 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((app) => {
+  const collection = new Collection({
+    "createRule": "@request.auth.verein_id = verein_id",
+    "deleteRule": "@request.auth.verein_id = verein_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": "pbc_3589557411",
+        "help": "",
+        "hidden": false,
+        "id": "relation145676011",
+        "maxSelect": 1,
+        "minSelect": 0,
+        "name": "verein_id",
+        "presentable": false,
+        "required": true,
+        "system": false,
+        "type": "relation"
+      },
+      {
+        "autogeneratePattern": "",
+        "help": "",
+        "hidden": false,
+        "id": "text1579384326",
+        "max": 0,
+        "min": 0,
+        "name": "name",
+        "pattern": "",
+        "presentable": false,
+        "primaryKey": false,
+        "required": true,
+        "system": false,
+        "type": "text"
+      },
+      {
+        "help": "",
+        "hidden": false,
+        "id": "number3107246631",
+        "max": null,
+        "min": null,
+        "name": "betrag",
+        "onlyInt": false,
+        "presentable": false,
+        "required": true,
+        "system": false,
+        "type": "number"
+      },
+      {
+        "help": "",
+        "hidden": false,
+        "id": "select917011370",
+        "maxSelect": 1,
+        "name": "rhythmus",
+        "presentable": false,
+        "required": true,
+        "system": false,
+        "type": "select",
+        "values": [
+          "monatlich",
+          "quartalsweise",
+          "jaehrlich",
+          "einmalig"
+        ]
+      }
+    ],
+    "id": "pbc_3218207135",
+    "indexes": [],
+    "listRule": "@request.auth.verein_id = verein_id",
+    "name": "beitraege",
+    "system": false,
+    "type": "base",
+    "updateRule": "@request.auth.verein_id = verein_id",
+    "viewRule": "@request.auth.verein_id = verein_id"
+  });
+
+  return app.save(collection);
+}, (app) => {
+  const collection = app.findCollectionByNameOrId("pbc_3218207135");
+
+  return app.delete(collection);
+})