Schedule message (#15)

Reviewed-on: phoenix/textsender_api#15

migrations/20260613211440_init.sql

@@ -16,3 +16,11 @@ CREATE TABLE IF NOT EXISTS "messages" (
     content TEXT NOT NULL,
     user_id UUID NOT NULL
 );
+
+CREATE TABLE IF NOT EXISTS "scheduled_messages" (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    scheduled timestamptz NOT NULL,
+    created timestamptz DEFAULT now(),
+    status TEXT CHECK (status IN ('PENDING', 'READY', 'PROCESSING', 'DONE')),
+    user_id UUID NOT NULL
+);