Schema 1.4.0: drop meta.sessions.json

The definition string is the only stored schedule. The "json" column held a
parsed copy that the Python client wrote, the C++ client never wrote, and
neither client read -- and a raw UPDATE of one field silently left two
different schedules. Clients derive the parsed form from the definition.
09_schema_check.sql no longer expects the column; VERSION and
10_schema_version.sql at 1.4.0. Re-provision databases (no migrations).

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

sql/03_tables.sql

@@ -128,10 +128,13 @@ CREATE TABLE meta.series (
     needs_reindex boolean NOT NULL DEFAULT false
 );
 
+-- A session's schedule is its definition string, nothing else. (Until 1.4.0
+-- a parsed copy was also stored in a "json" column; nothing read it, the C++
+-- client never wrote it, and it could silently disagree with the definition.
+-- Clients derive the parsed form from the definition when they need it.)
 CREATE TABLE meta.sessions (
     name character varying(50) NOT NULL,
     definition text NOT NULL,
-    "json" text,
     exchange_id character varying(12) NOT NULL
 );