refactor(models): update data models and remove deprecated IM entities

- Update channel, notification, PR, repo, user, workspace models
- Remove deleted IM models: articles, channel follows, message
  attachments/bookmarks/drafts/edit history/embeds/mentions/pins/
  polls/reactions/threads, saved messages, thread read states
- Add new PR models: review requests, templates
- Add repo release assets model
- Add base_info module for API detail responses

models/prs/pr_review_requests.rs

@@ -0,0 +1,11 @@
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, sqlx::FromRow, utoipa::ToSchema)]
+pub struct PrReviewRequest {
+    pub id: Uuid,
+    pub pull_request_id: Uuid,
+    pub reviewer_id: Uuid,
+    pub requested_by: Uuid,
+    pub created_at: chrono::DateTime<chrono::Utc>,
+}