halkyon_base: a Serverpod module for sign-in, accounts and instance basics

What every Halkyon server has, taken from Halkyon Learn's: anonymous,
GitHub and email-code sign-in with their endpoints, an account's ways
in and its deletion, the pruning of abandoned anonymous people, of
sign-up attempts and of expired codes, and the instance's basics (the
sign-in ways offered, the source link, the minimum app build, where
people's data and its backups are). Endpoints sit under the nickname
`base`. A host configures it in one place before its pod starts: its
name for the mails, its source link, its minimum build, and hooks that
delete its own data with a person.

The tables keep Learn's names, columns and indexes, so a host moving
onto the module migrates nothing but version rows. Server package under
the SSPL, client under the AGPL, as Learn's are.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_base_server/test/unit/source_code_test.dart

@@ -0,0 +1,19 @@
+import 'package:halkyon_base_server/base.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test("the operator's source URL counts only where they set one", () {
+    expect(
+      sourceCodeUrlFrom('https://code.example.org/fork'),
+      'https://code.example.org/fork',
+    );
+    expect(
+      sourceCodeUrlFrom('  https://code.example.org/fork '),
+      'https://code.example.org/fork',
+    );
+    // Compose passes unset variables on as empty strings.
+    expect(sourceCodeUrlFrom(''), isNull);
+    expect(sourceCodeUrlFrom('   '), isNull);
+    expect(sourceCodeUrlFrom(null), isNull);
+  });
+}