fix: idempotent migrations (ADD COLUMN IF NOT EXISTS), stale doc, safety note

hive-c0re/src/stores/operator_questions.rs

@@ -39,13 +39,14 @@ CREATE INDEX IF NOT EXISTS idx_operator_questions_pending
 /// past all known migrations.
 const MIGRATIONS: &[&str] = &[
     // v1: `multi` — checkbox-style multi-option questions.
-    "ALTER TABLE operator_questions ADD COLUMN multi INTEGER NOT NULL DEFAULT 0",
+    "ALTER TABLE operator_questions ADD COLUMN IF NOT EXISTS \
+     multi INTEGER NOT NULL DEFAULT 0",
     // v2: `deadline_at` — optional TTL after which the watchdog auto-resolves.
-    "ALTER TABLE operator_questions ADD COLUMN deadline_at INTEGER",
+    "ALTER TABLE operator_questions ADD COLUMN IF NOT EXISTS deadline_at INTEGER",
     // v3: `target` — recipient of the question. NULL = operator (back-compat
     // default); non-null = peer-to-peer question. Dashboard's `pending()`
     // filters on `target IS NULL` so peer questions never leak to the operator.
-    "ALTER TABLE operator_questions ADD COLUMN target TEXT",
+    "ALTER TABLE operator_questions ADD COLUMN IF NOT EXISTS target TEXT",
 ];
 
 #[derive(Debug, Clone, Serialize)]