[DO NOT MERGE] Email notification system (#4338)

* Migration

* Fixup db models

* Redis

* Stuff

* Switch PKs to BIGSERIALs, insert to notifications_deliveries when inserting notifications

* Queue, templates

* Query cache

* Fixes, fixtures

* Perf, cache template data & HTML bodies

* Notification type configuration, ResetPassword notification type

* Reset password

* Query cache

* Clippy + fmt

* Traces, fix typo, fix user email in ResetPassword

* send_email

* Models, db

* Remove dead code, adjust notification settings in migration

* Clippy fmt

* Delete dead code, fixes

* Fmt

* Update apps/labrinth/src/queue/email.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Remove old fixtures

* Unify email retry delay

* Fix type

* External notifications

* Remove `notifications_types_preference_restrictions`, as user notification preferences is out of scope for this PR

* Query cache, fmt, clippy

* Fix join in get_many_user_exposed_on_site

* Remove migration comment

* Query cache

* Update html body urls

* Remove comment

* Add paymentfailed.service variable to PaymentFailed notification variant

* Fix compile error

* Fix deleting notifications

* Update apps/labrinth/src/database/models/user_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update apps/labrinth/src/database/models/user_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update Cargo.toml

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update apps/labrinth/migrations/20250902133943_notification-extension.sql

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Address review comments

* Fix compliation

* Update apps/labrinth/src/database/models/users_notifications_preferences_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Use strfmt to format emails

* Configurable Reply-To

* Configurable Reply-To

* Refactor for email background task

* Send some emails inline

* Fix account creation email check

* Revert "Use strfmt to format emails"

This reverts commit e0d6614afe51fa6349918377e953ba294c34ae0b.

* Reintroduce fill_template

* Set password reset email inline

* Process more emails per index

* clippy fmt

* Query cache

---------

Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Josiah Glosson <soujournme@gmail.com>

apps/labrinth/src/background_task.rs

@@ -1,4 +1,5 @@
 use crate::database::redis::RedisPool;
+use crate::queue::email::EmailQueue;
 use crate::queue::payouts::{
     PayoutsQueue, insert_bank_balances_and_webhook, process_payout,
 };
@@ -18,6 +19,7 @@ pub enum BackgroundTask {
     IndexBilling,
     IndexSubscriptions,
     Migrations,
+    Mail,
 }
 
 impl BackgroundTask {
@@ -28,6 +30,7 @@ impl BackgroundTask {
         search_config: search::SearchConfig,
         clickhouse: clickhouse::Client,
         stripe_client: stripe::Client,
+        email_queue: EmailQueue,
     ) {
         use BackgroundTask::*;
         match self {
@@ -52,10 +55,19 @@ impl BackgroundTask {
                 )
                 .await
             }
+            Mail => {
+                run_email(email_queue).await;
+            }
         }
     }
 }
 
+pub async fn run_email(email_queue: EmailQueue) {
+    if let Err(error) = email_queue.index().await {
+        error!(%error, "Failed to index email queue");
+    }
+}
+
 pub async fn update_bank_balances(pool: sqlx::Pool<Postgres>) {
     let payouts_queue = PayoutsQueue::new();