feat: Add created_at, updated_at fields in the db proposal model

heromodels/examples/governance_proposal_example/main.rs

@@ -18,6 +18,8 @@ fn main() {
         "Ahmed fared",                      // creator_id
         "Community Fund Allocation for Q3", // title
         "Proposal to allocate funds for community projects in the third quarter.", // description
+        Utc::now(),                         // created_at
+        Utc::now(),                         // updated_at
         Utc::now(),                         // vote_start_date
         Utc::now() + Duration::days(14),    // vote_end_date (14 days from now)
     );
@@ -130,6 +132,8 @@ fn main() {
         "Internal Team Restructure Vote",
         "Vote on proposed internal team changes.",
         Utc::now(),
+        Utc::now(),
+        Utc::now(),
         Utc::now() + Duration::days(7),
     );
     private_proposal.private_group = Some(vec![10, 20, 30]); // Only users 10, 20, 30 can vote