Add generated SQL columns for graph properties

AGE keeps all properties in one agtype column and its Cypher writes fire
no triggers, so the bridge periodically calls a stored procedure that adds
a stored generated text column for every new property key. Only label
tables with inserts or updates since the previous run are scanned.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bridge/peo4c/backend.py

@@ -337,6 +337,9 @@ class Session:
             raise BoltFailure("Neo.ClientError.Statement.ArgumentError",
                               f"Invalid graph name '{name}': AGE graph names must be 3-63 characters "
                               "of letters, digits, '_', '.' or '-', starting with a letter or '_'.")
+        if name == "peo4c":
+            raise BoltFailure("Neo.ClientError.Statement.ArgumentError",
+                              "The name 'peo4c' is reserved: it is the schema of peo4c's own SQL helpers.")
         if name in await self.graphs():
             if if_not_exists:
                 return Result([], query_type="s")