Parenthesize chunk retention CASE expressions in PL/pgSQL IF guards (#99)

Database bootstrap currently fails with PostgreSQL 42601 at Original(10355): the first unparenthesized CASE in a PL/pgSQL IF exposes its internal THEN as the end of the IF condition. Parenthesize that CASE and the identical later map guard expression. Preserve both 512 MiB capacity checks, state-dependent 256 KiB/1 MiB reserves, error messages and every other migration byte. Exact original source-offset and whole-file inverse proofs plus whitespace and unchanged-tree checks pass. The cancelled native run has no completed test summary; this candidate has not executed SQL or native tests.

Author: Ivanbeethoven

src/jupiter/migration/m20261008_000300_chunk_map_retention.sql

@@ -152,7 +152,7 @@ BEGIN
   IF TG_OP='DELETE' OR TG_OP='TRUNCATE' THEN
     RAISE EXCEPTION 'chunk receipt generations and collection history are retained';
   END IF;
-  IF mst2_chunk_retention_bytes()+CASE WHEN NEW.state IN ('DELETING','APPLIED') THEN 262144 ELSE 1048576 END>536870912 THEN
+  IF mst2_chunk_retention_bytes()+(CASE WHEN NEW.state IN ('DELETING','APPLIED') THEN 262144 ELSE 1048576 END)>536870912 THEN
     RAISE EXCEPTION 'chunk receipt mutation lacks actual durable byte headroom';
   END IF;
   IF TG_OP='UPDATE' AND (NEW.receipt_key IS DISTINCT FROM OLD.receipt_key OR NEW.source_id IS DISTINCT FROM OLD.source_id
@@ -244,7 +244,7 @@ BEGIN
     IF NOT permitted THEN RAISE EXCEPTION 'map lifetime deletion lacks exact reader-free collection claim'; END IF;
     RETURN OLD;
   END IF;
-  IF mst2_chunk_retention_bytes()+CASE WHEN NEW.state='DELETING' THEN 262144 ELSE 1048576 END>536870912 THEN
+  IF mst2_chunk_retention_bytes()+(CASE WHEN NEW.state='DELETING' THEN 262144 ELSE 1048576 END)>536870912 THEN
     RAISE EXCEPTION 'chunk map lifetime mutation lacks actual durable byte headroom';
   END IF;
   IF TG_OP='UPDATE' AND (NEW.map_id IS DISTINCT FROM OLD.map_id OR NEW.generation IS DISTINCT FROM OLD.generation