fix: clean up church-matcher types and add HK OSM bounding box

- Remove discovermassId/buscarmisasNetworkId from findDuplicateChurch match
  passes (importers now do their own pre-check dedup); restore as optional
  fields on ExistingChurch to keep type/runtime in sync
- Add HK bounding box to COUNTRY_BOUNDING_BOXES; fix silent 0-result
  fallback when country query returns empty from mirror server
- discovermass importer: add --limit flag and skip-already-imported
  pre-check using importedSlugs set
- Import scripts: remove discovermassId from ExistingChurch select/stubs
  (field not needed in shared matcher context)
- Schema: reorder discovermassId/kerknetId/gottesdienstzeitenId fields

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/import-miserend.ts

@@ -240,7 +240,6 @@ async function loadExistingChurches(countryCodes: string[]): Promise<ExistingChu
       miserendId: true,
       kerknetId: true,
       gottesdienstzeitenId: true,
-      discovermassId: true,
       source: true,
       website: true,
       phone: true,
@@ -366,7 +365,6 @@ async function processChurch(
         miserendId,
         kerknetId: null,
         gottesdienstzeitenId: null,
-        discovermassId: null,
         source: 'miserend',
         website: null,
         phone: null,