Decouple cross-domain DB queries for per-app database split

Move Ghost membership sync from blog to account service so blog no
longer queries account tables (users, ghost_labels, etc.). Account
runs membership sync at startup and exposes HTTP action/data endpoints
for webhook-triggered syncs and user lookups.

Key changes:
- account/services/ghost_membership.py: all membership sync functions
- account/bp/actions + data: ghost-sync-member, user-by-email, newsletters
- blog ghost_sync.py: stripped to content-only (posts, authors, tags)
- blog webhook member: delegates to account via call_action()
- try_publish: opens federation session when DBs differ
- oauth.py callback: uses get_account_session() for OAuthCode
- page_configs moved from db_events to db_blog in split script

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

_config/move-page-configs.sql

@@ -0,0 +1,17 @@
+-- Move page_configs data from db_events to db_blog.
+-- Run after split-databases.sh if page_configs data ended up in db_events.
+--
+-- Usage:
+--   PGHOST=db PGUSER=postgres PGPASSWORD=change-me psql -f move-page-configs.sql
+--
+
+-- Step 1: Dump page_configs from db_events into db_blog
+\c db_events
+COPY page_configs TO '/tmp/page_configs.csv' WITH CSV HEADER;
+
+\c db_blog
+TRUNCATE page_configs;
+COPY page_configs FROM '/tmp/page_configs.csv' WITH CSV HEADER;
+
+-- Step 2: Verify
+SELECT count(*) AS blog_page_configs FROM page_configs;

_config/split-databases.sh

@@ -42,6 +42,7 @@ DB_TABLES[db_blog]="
   menu_items
   menu_nodes
   container_relations
+  page_configs
 "
 
 DB_TABLES[db_market]="
@@ -78,7 +79,6 @@ DB_TABLES[db_events]="
   calendar_entry_posts
   ticket_types
   tickets
-  page_configs
 "
 
 DB_TABLES[db_federation]="