feat: HA scheduler leadership + templated email log

HA scheduler: the job scheduler and alert evaluator hold session-scoped
PostgreSQL advisory locks on pinned pool connections — replicas scan for
due work exactly once, failover verified live with two replicas. Manual
and hook-triggered runs stay available on any replica.

Email surface: mailer renders registered templates (invitation); every
send is logged to core.email_log with status and error text. New
GET /projects/:id/emails endpoint; Members page shows an Email log card.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/database/db/querier.go

@@ -84,6 +84,7 @@ type Querier interface {
 	GetWebhookByID(ctx context.Context, id uuid.UUID) (CoreWebhook, error)
 	GetWebhookDeliveryByID(ctx context.Context, id uuid.UUID) (CoreWebhookDelivery, error)
 	HasFingerprintSeen(ctx context.Context, arg HasFingerprintSeenParams) (bool, error)
+	InsertEmailLog(ctx context.Context, arg InsertEmailLogParams) (CoreEmailLog, error)
 	InsertEvent(ctx context.Context, arg InsertEventParams) (CoreEvent, error)
 	InsertScheduledJobRun(ctx context.Context, arg InsertScheduledJobRunParams) (CoreScheduledJobRun, error)
 	InsertWebhookDelivery(ctx context.Context, arg InsertWebhookDeliveryParams) (CoreWebhookDelivery, error)
@@ -100,6 +101,7 @@ type Querier interface {
 	ListDBConnections(ctx context.Context, projectID uuid.UUID) ([]CoreDbConnection, error)
 	ListDocuments(ctx context.Context, arg ListDocumentsParams) ([]CoreDocument, error)
 	ListDueScheduledJobs(ctx context.Context, nextRunAt pgtype.Timestamptz) ([]CoreScheduledJob, error)
+	ListEmailLog(ctx context.Context, arg ListEmailLogParams) ([]CoreEmailLog, error)
 	ListEnabledAlertRules(ctx context.Context) ([]CoreAlertRule, error)
 	ListErrorGroups(ctx context.Context, arg ListErrorGroupsParams) ([]ListErrorGroupsRow, error)
 	ListEvents(ctx context.Context, arg ListEventsParams) ([]ListEventsRow, error)