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/CHANGELOG.md

@@ -0,0 +1,8 @@
+## 0.1.0
+
+* What every Halkyon server has, from Halkyon Learn's server: anonymous,
+  GitHub and email code sign-in with their endpoints, the account's ways in
+  and its deletion (with the host's own deletions, `HalkyonBase.deletePersonData`),
+  the pruning of abandoned anonymous people, of sign-up attempts and of
+  expired codes, and the instance's basics (`instance.basics()`). The tables
+  `email_identity` and `email_code_request` are as Halkyon Learn has them.