Improve mailer performance

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/coredata/migrations/20260308T120000Z.sql

@@ -0,0 +1,12 @@
+ALTER TABLE emails
+ADD COLUMN status TEXT NOT NULL DEFAULT 'PENDING',
+ADD COLUMN processing_started_at TIMESTAMP WITH TIME ZONE,
+ADD COLUMN attempt_count INTEGER NOT NULL DEFAULT 0,
+ADD COLUMN max_attempts INTEGER NOT NULL DEFAULT 10,
+ADD COLUMN last_attempted_at TIMESTAMP WITH TIME ZONE,
+ADD COLUMN last_error TEXT;
+
+UPDATE emails SET status = 'SENT' WHERE sent_at IS NOT NULL;
+
+CREATE INDEX idx_emails_pending ON emails (status, created_at)
+WHERE status = 'PENDING';