feat: add join form settings

docs/development-progress-log.md

@@ -809,8 +809,13 @@ end
 - **PR review follow-ups (Join confirmation):** Join confirmation email uses `Mailer.deliver/1` and returns `{:ok, email}` \| `{:error, reason}`; domain logs delivery errors but still returns `{:ok, request}` so the user sees success. Comment in `submit_join_request/2` clarifies that the raw token is hashed by `JoinRequest.Changes.SetConfirmationToken`. Cleanup task uses `Ash.bulk_destroy` and logs partial errors without halting. Layout uses assigns `app_name` and `locale` (from config/Gettext) instead of hardcoded "Mila" and `lang="de"`. Production `runtime.exs` sets `:mail_from` from ENV (`MAIL_FROM_NAME`, `MAIL_FROM_EMAIL`). Layout reference unified to `"layout.html"`; redundant `put_layout` removed from senders.
 - Tests: `join_request_test.exs`, `join_request_submit_email_test.exs`, `join_confirm_controller_test.exs` – all pass.
 
-**Subtask 3 – Admin: Join form settings (TDD tests only):**
-- Test file: `test/membership/setting_join_form_test.exs` – TDD tests for join form settings (persistence, validation, allowlist, defaults, robustness). Tests are red until Setting gains `join_form_enabled`, `join_form_field_ids`, `join_form_field_required` and `Mv.Membership.get_join_form_allowlist/0` is implemented. No functionality implemented yet.
+**Subtask 3 – Admin: Join form settings (done):**
+- **Setting resource** (`lib/membership/setting.ex`): 3 new attributes `join_form_enabled` (boolean, default false), `join_form_field_ids` ({:array, :string} – ordered list of member field names or custom field UUIDs), `join_form_field_required` (:map – field ID → boolean). Added to `:create` and `:update` accept lists. Validation rejects field IDs that are neither valid member field names nor UUID format. Migration: `20260310114701_add_join_form_settings_to_settings.exs`.
+- **NormalizeJoinFormSettings** (`lib/membership/setting/changes/normalize_join_form_settings.ex`): Change applied on create/update whenever join form attrs are changing. Ensures email is always in `join_form_field_ids`, forces `join_form_field_required["email"] = true`, drops required flags for fields not in `join_form_field_ids`.
+- **Domain** (`lib/membership/membership.ex`): `Mv.Membership.get_join_form_allowlist/0` – returns `[]` when join form is disabled, otherwise a list of `%{id, required, type}` maps (type = `:member_field` or `:custom_field` based on ID format).
+- **GlobalSettingsLive** (`lib/mv_web/live/global_settings_live.ex`): New "Join Form" / "Beitrittsformular" section between Club Settings and Vereinfacht. Checkbox to enable/disable, table of selected fields (with Required checkbox per field – email always checked/disabled, other fields can be toggled), "Add field" dropdown with all unselected member fields and custom fields, "Save Join Form Settings" button. State is managed locally (not via AshPhoenix.Form); saved on explicit save click.
+- **Translations**: 14 new German strings in `priv/gettext/de/LC_MESSAGES/default.po` (Beitrittsformular, Felder im Beitrittsformular, Feld hinzufügen, etc.).
+- Tests: All 13 tests in `test/membership/setting_join_form_test.exs` pass; full test suite 1900 tests, 0 failures.
 
 ### Test Data Management