refactor(cron): normalize payload columns into dedicated DB fields (#33)

Extract wake_heartbeat and stateless from JSON payload into first-class
columns on cron_jobs. Adds migration 000033 with backfill from existing
payload data. Updates PG + SQLite stores, RPC handlers, and UI i18n.

internal/store/sqlitestore/schema.sql

@@ -449,6 +449,11 @@ CREATE TABLE IF NOT EXISTS cron_jobs (
     timezone         VARCHAR(50),
     payload          TEXT NOT NULL,
     delete_after_run BOOLEAN NOT NULL DEFAULT 0,
+    stateless        INTEGER NOT NULL DEFAULT 0,
+    deliver          INTEGER NOT NULL DEFAULT 0,
+    deliver_channel  TEXT NOT NULL DEFAULT '',
+    deliver_to       TEXT NOT NULL DEFAULT '',
+    wake_heartbeat   INTEGER NOT NULL DEFAULT 0,
     next_run_at      TEXT,
     last_run_at      TEXT,
     last_status      VARCHAR(20),