feat: Background tasks table + tasks route migrated to Rust

- New migration: background_tasks table
- New model: BackgroundTask (background_task.rs)
- GET /api/tasks with limit param
- GET /api/tasks/{id} with 404 handling
- 18/18 tests pass

boosapi-rs/src/db/models/background_task.rs

@@ -0,0 +1,25 @@
+use serde::{Deserialize, Serialize};
+use sqlx::FromRow;
+
+/// Background task for tracking async operations (deployments, syncs, etc.)
+#[derive(Debug, Clone, Serialize, Deserialize, FromRow)]
+pub struct BackgroundTask {
+    pub id: String,
+    pub task_type: String,
+    pub title: String,
+    pub status: String,
+    pub message: Option<String>,
+    pub error: Option<String>,
+    pub dedupe_key: Option<String>,
+    pub success_title: Option<String>,
+    pub failure_title: Option<String>,
+    pub notify_on_success: Option<bool>,
+    pub notify_on_failure: Option<bool>,
+    pub result_json: Option<String>,
+    pub progress: Option<i64>,
+    pub progress_total: Option<i64>,
+    pub created_at: Option<String>,
+    pub updated_at: Option<String>,
+    pub started_at: Option<String>,
+    pub finished_at: Option<String>,
+}

boosapi-rs/src/db/models/mod.rs

@@ -7,5 +7,6 @@ pub mod route_channel;
 pub mod setting;
 pub mod site;
 pub mod site_announcement;
+pub mod background_task;
 pub mod token_route;
 pub mod user;