security: enforce https on dues_payment_methods.url at the data layer

The url renders to members as a clickable href. https was enforced only
in the admin Zod action, but RLS lets an admin/board write the row
directly via PostgREST, bypassing Zod, with no DB constraint -- a
malicious admin could store a javascript: URL and XSS members who click.

- Migration 050: CHECK (url ~* '^https://') so the DB is the source of
  truth; integration-tested that the service path cannot store
  javascript:/http:.
- Member-read action filters with isSafeDuesUrl (defense-in-depth).

docs/DATABASE_SCHEMA.md

@@ -730,6 +730,7 @@ migration is mirrored as a section in it. Tables/columns added:
 | 047 | `members_with_permission(sid, perm)` SECURITY DEFINER, `search_path=public`. Inverted, set-returning form of `user_has_permission`: returns `member_id` for every member of `sid` who holds `perm` (same current/late status gate as 046, same admin shortcut, same `space_role_permissions` + `user_effective_roles` fallback). Lets the Phase 4 notification fan-outs (e.g. `form_submission_admin`) find permission holders in one query instead of N round-trips. EXECUTE is locked: `REVOKE EXECUTE FROM PUBLIC`, `GRANT EXECUTE TO service_role` so the set-returning shape cannot be used by a PostgREST client to enumerate "who has permission X in space Y" across spaces (the rationale for not locking `user_has_permission` is that RLS policies depend on anon/authenticated being able to call it). Additive; existing `user_has_permission` callers unchanged. No new table/column/policy |
 | 048 | `notification_preferences` (Product spine Phase 5): per-member opt-out of muteable categories. Columns `space_id, member_id, category, enabled`, PK `(space_id, member_id, category)`. Opt-out model: absence of a row = enabled. Only the four muteable categories (`bookings, classes, forms, admin_alerts`) are ever stored; `billing` (dues renewed/failed/lapsed) is membership-critical and never muteable. RLS enabled, NO client policy (default-deny): the dispatcher reads via the service client and marks a muted outbox row `skipped`; the `/me` self-view + toggle write both go through validated service-client actions, same convention as `notifications` / `member_billing`. `touch_updated_at` trigger. No new permission code |
 | 049 | `dues_payment_methods`: admin-configured external dues payment links. Columns `id, space_id, platform (payment_platform), url, instructions, is_active, sort_order`, `UNIQUE (space_id, platform)`. One external pay-here URL per platform (PayPal/Zeffy/Venmo); members click out to pay dues off-platform and a treasurer reconciles manually via the existing payments flow (the platform tag pre-types that reconcile). Link configuration only, no automated payment record. RLS: SELECT = any space member (they render the buttons); INSERT/UPDATE/DELETE = admin/board (`user_has_role_in_space`). `url` is validated absolute-https at the server-action boundary. `touch_updated_at` trigger. No new permission code |
+| 050 | `dues_payment_methods.url` gains a CHECK constraint (`dues_payment_methods_url_https`, `url ~* '^https://'`). The url is rendered to members as a clickable href; RLS lets an admin/board write the row directly via PostgREST, bypassing the app Zod check, so the DB enforces https as the source of truth (a `javascript:`/`http:` value can never be stored). The member-read action also re-validates with `isSafeDuesUrl` (defense-in-depth). Idempotent DO-block add-if-missing. No new table/column/policy |
 
 New enum: `comment_entity_type` = `forum_thread | proposal | incident | policy`.