refactor(schema): fan desired-state schema out to one file per table (#8131)

schema/functions/community_write_allowed.sql

@@ -0,0 +1,24 @@
+-- Fleet-wide writers filter candidates through this VOLATILE predicate in
+-- the mutating statement so fenced tenants are skipped before row triggers run.
+CREATE FUNCTION community_write_allowed(target UUID) RETURNS BOOLEAN
+LANGUAGE plpgsql VOLATILE AS $$
+DECLARE
+    lifecycle TEXT;
+BEGIN
+    IF current_setting('transaction_isolation') <> 'read committed' THEN
+        RAISE EXCEPTION 'community writes require READ COMMITTED isolation'
+            USING ERRCODE = 'invalid_transaction_state';
+    END IF;
+
+    IF target IS NULL THEN
+        RETURN true;
+    END IF;
+
+    PERFORM pg_advisory_xact_lock_shared(community_deletion_lock_key(target));
+    SELECT deletion_state
+      INTO lifecycle
+      FROM communities
+     WHERE id = target;
+    RETURN FOUND AND lifecycle = 'active';
+END
+$$;