ZXDB: Add Phase A schema models and list APIs; align repo

- Schema: add Drizzle models for availabletypes, currencies, roletypes, issues, magazines, role relations
- Repo: add list/search functions for new lookups (availabletypes, currencies, roletypes)
- API: expose /api/zxdb/{availabletypes,currencies,roletypes} list endpoints
- UI: (deferred) existing pages can now populate dropdowns with proper names where needed
- Keeps previous releases/downloads fixes intact

Signed-off-by: Junie@HOSTNAME