refactor(hive-c0re): shared additive-migration helper in db

db::apply_migrations runs ALTER lists and ignores duplicate-column
errors (turn_stats' pattern); approvals, operator_questions, broker
reminders, and scheduled_prompts drop their hand-rolled
pragma_table_info guards. broker's acked_at migration stays bespoke —
its backfill must only run when the column was just created

hive-c0re/src/broker.rs

@@ -1121,33 +1121,19 @@ fn ensure_message_columns(conn: &Connection) -> Result<()> {
     Ok(())
 }
 
-/// Idempotent reminder-table migrations. `ALTER TABLE ADD COLUMN`
-/// has no `IF NOT EXISTS` form in sqlite, so we probe
-/// `pragma_table_info` per column. New deploys (table created by
-/// SCHEMA in this commit cycle) skip the ALTER; pre-existing
-/// broker.sqlite files get the columns added on next boot.
+/// Idempotent reminder-table migrations — plain additive columns, via
+/// `db::apply_migrations`. (The messages-table migration above stays
+/// bespoke: its backfill must run only when `acked_at` was just
+/// created, which try-and-ignore can't express.)
 fn ensure_reminder_columns(conn: &Connection) -> Result<()> {
-    for (name, sql) in [
-        (
-            "attempt_count",
-            "ALTER TABLE reminders ADD COLUMN attempt_count INTEGER NOT NULL DEFAULT 0;",
-        ),
-        (
-            "last_error",
-            "ALTER TABLE reminders ADD COLUMN last_error TEXT;",
-        ),
-    ] {
-        let has: bool = conn
-            .prepare(&format!(
-                "SELECT 1 FROM pragma_table_info('reminders') WHERE name = '{name}'"
-            ))?
-            .exists([])?;
-        if !has {
-            conn.execute_batch(sql)
-                .with_context(|| format!("add reminders.{name} column"))?;
-        }
-    }
-    Ok(())
+    crate::db::apply_migrations(
+        conn,
+        "broker reminders",
+        &[
+            "ALTER TABLE reminders ADD COLUMN attempt_count INTEGER NOT NULL DEFAULT 0",
+            "ALTER TABLE reminders ADD COLUMN last_error TEXT",
+        ],
+    )
 }
 
 fn now_unix() -> i64 {