feat: join request backend

docs/development-progress-log.md

@@ -335,6 +335,15 @@ end
 - show custom fields in member overview per default
 - can be set to false in the settings for the specific custom field
 
+---
+
+**Onboarding / Public Join (Issue #308) – Subtask 1: JoinRequest resource and public policies**
+- JoinRequest Ash resource (`lib/membership/join_request.ex`) per concept §2.3.2: email, confirmation_token_hash, status, submitted_at, source, schema_version, payload, approved_at, rejected_at, reviewed_by_user_id
+- Migration `20260220120000_add_join_requests.exs` with unique index on `confirmation_token_hash` for idempotency
+- Public policies: `:confirm` and `:read` allowed with `actor: nil`; generic `:create` requires HasPermission
+- Domain interface: `confirm_join_request/2`, `list_join_requests/1`, `get_join_request/2`, `update_join_request/2`, `destroy_join_request/1`
+- Tests: `test/mv/membership/join_request_test.exs` – public create/read with nil, idempotency, validations (no UI/email yet)
+
 ## Implementation Decisions
 
 ### Architecture Patterns