Add PocketBase client with contracts and containerized tests

Elternbeirat.Web.Tests/.editorconfig

@@ -6,3 +6,14 @@
 # common, readable convention for tests. CA1707 (no underscores in member names)
 # stays enforced in production code, but is turned off here.
 dotnet_diagnostic.CA1707.severity = none
+
+# CA1861 wants constant array arguments hoisted to static readonly fields to avoid
+# re-allocation. In one-time test setup (collection seeding) that micro-optimization
+# has no benefit and inline arrays keep the seed data readable.
+dotnet_diagnostic.CA1861.severity = none
+
+# CA1001 wants a type with a disposable field to implement IDisposable. The xunit
+# fixture already owns and disposes its fields in IAsyncLifetime.DisposeAsync, which
+# xunit calls; the analyzer just does not recognize that as the dispose contract.
+# Adding IAsyncDisposable clashes with IAsyncLifetime's Task-returning DisposeAsync.
+dotnet_diagnostic.CA1001.severity = none