Phase 19: persistent notifications system

New notifications table (migration 0009) stores event-driven alerts
alongside the existing dynamic state notifications (unclaimed objectives,
expiring loans, season ending soon).

Persistent notifications are created automatically during match
processing: one per level gained, one per expired loan card, one per
objective newly completed, and one when a season ends (with
promotion/relegation result and rewards in the body).

GET /notifications now returns a merged list — persistent entries
(newest-first, limit 50) followed by dynamic entries — plus an
unread_count for the badge. Each item carries type, title, body,
is_read, and (for persistent) id and created_at.

PATCH /notifications/:id/read marks a single persistent notification
read. POST /notifications/read-all marks all persistent ones read.

Four new tests: unread_count field, level-up notification creation,
mark-all-read, single-read PATCH. Core now at 77 tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/notification.rs

@@ -0,0 +1,49 @@
+use crate::{db::Pool, error::AppResult, models::notification::Notification};
+
+pub async fn create(pool: &Pool, kind: &str, title: &str, body: &str) -> AppResult<()> {
+    let n = Notification::new(kind, title, body);
+    sqlx::query(
+        "INSERT INTO notifications (id, kind, title, body, is_read, created_at) \
+         VALUES (?, ?, ?, ?, 0, ?)",
+    )
+    .bind(&n.id)
+    .bind(&n.kind)
+    .bind(&n.title)
+    .bind(&n.body)
+    .bind(&n.created_at)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+pub async fn list(pool: &Pool) -> AppResult<Vec<Notification>> {
+    sqlx::query_as::<_, Notification>(
+        "SELECT id, kind, title, body, is_read, created_at \
+         FROM notifications ORDER BY created_at DESC LIMIT 50",
+    )
+    .fetch_all(pool)
+    .await
+    .map_err(Into::into)
+}
+
+pub async fn mark_read(pool: &Pool, id: &str) -> AppResult<bool> {
+    let r = sqlx::query("UPDATE notifications SET is_read = 1 WHERE id = ?")
+        .bind(id)
+        .execute(pool)
+        .await?;
+    Ok(r.rows_affected() > 0)
+}
+
+pub async fn mark_all_read(pool: &Pool) -> AppResult<i64> {
+    let r = sqlx::query("UPDATE notifications SET is_read = 1 WHERE is_read = 0")
+        .execute(pool)
+        .await?;
+    Ok(r.rows_affected() as i64)
+}
+
+pub async fn unread_count(pool: &Pool) -> AppResult<i64> {
+    sqlx::query_scalar("SELECT COUNT(*) FROM notifications WHERE is_read = 0")
+        .fetch_one(pool)
+        .await
+        .map_err(Into::into)
+}