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/repos/repo_release_assets.rs

@@ -0,0 +1,19 @@
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, sqlx::FromRow, utoipa::ToSchema)]
+pub struct RepoReleaseAsset {
+    pub id: Uuid,
+    pub release_id: Uuid,
+    pub filename: String,
+    pub size_bytes: i64,
+    pub mime_type: String,
+    pub storage_path: String,
+    pub url: Option<String>,
+    pub download_count: i64,
+    pub uploaded_by: Option<Uuid>,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+    pub deleted_at: Option<DateTime<Utc>>,
+}