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>

shared/services/federation_publish.py

@@ -4,6 +4,9 @@ The originating service calls try_publish() directly, which creates the
 APActivity (with process_state='pending') in the same DB transaction.
 The EventProcessor picks it up and the delivery wildcard handler POSTs
 to follower inboxes.
+
+When the federation database is separate from the caller's database,
+this module opens its own federation session for all AP reads/writes.
 """
 from __future__ import annotations
 
@@ -17,6 +20,12 @@ from shared.services.registry import services
 log = logging.getLogger(__name__)
 
 
+def _needs_federation_session() -> bool:
+    """True when the federation DB differs from the app's default DB."""
+    from shared.db.session import DATABASE_URL, DATABASE_URL_FEDERATION
+    return DATABASE_URL_FEDERATION != DATABASE_URL
+
+
 async def try_publish(
     session: AsyncSession,
     *,
@@ -38,6 +47,42 @@ async def try_publish(
     if not user_id:
         return
 
+    if _needs_federation_session():
+        from shared.db.session import get_federation_session
+        async with get_federation_session() as fed_s:
+            async with fed_s.begin():
+                await _publish_inner(
+                    fed_s,
+                    user_id=user_id,
+                    activity_type=activity_type,
+                    object_type=object_type,
+                    object_data=object_data,
+                    source_type=source_type,
+                    source_id=source_id,
+                )
+    else:
+        await _publish_inner(
+            session,
+            user_id=user_id,
+            activity_type=activity_type,
+            object_type=object_type,
+            object_data=object_data,
+            source_type=source_type,
+            source_id=source_id,
+        )
+
+
+async def _publish_inner(
+    session: AsyncSession,
+    *,
+    user_id: int,
+    activity_type: str,
+    object_type: str,
+    object_data: dict,
+    source_type: str,
+    source_id: int,
+) -> None:
+    """Core publish logic using a session bound to the federation DB."""
     actor = await services.federation.get_actor_by_user_id(session, user_id)
     if not actor:
         return
@@ -48,28 +93,24 @@ async def try_publish(
     )
     if existing:
         if activity_type == "Create" and existing.activity_type != "Delete":
-            return  # already published (allow re-Create after Delete/unpublish)
+            return
         if activity_type == "Delete" and existing.activity_type == "Delete":
-            return  # already deleted
+            return
     elif activity_type in ("Delete", "Update"):
-        return  # never published, nothing to delete/update
+        return
 
-    # Stable object ID within a publish cycle.  After Delete + re-Create
-    # we append a version suffix so remote servers (Mastodon) treat it as
-    # a brand-new post rather than ignoring the tombstoned ID.
+    # Stable object ID within a publish cycle
     domain = os.getenv("AP_DOMAIN", "federation.rose-ash.com")
     base_object_id = (
         f"https://{domain}/users/{actor.preferred_username}"
         f"/objects/{source_type.lower()}/{source_id}"
     )
     if activity_type == "Create" and existing and existing.activity_type == "Delete":
-        # Count prior Creates to derive a version number
         create_count = await services.federation.count_activities_for_source(
             session, source_type, source_id, activity_type="Create",
         )
         object_data["id"] = f"{base_object_id}/v{create_count + 1}"
     elif activity_type in ("Update", "Delete") and existing and existing.object_data:
-        # Use the same object ID as the most recent activity
         object_data["id"] = existing.object_data.get("id", base_object_id)
     else:
         object_data["id"] = base_object_id