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/email_log.sql.go

@@ -0,0 +1,91 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.29.0
+// source: email_log.sql
+
+package db
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const insertEmailLog = `-- name: InsertEmailLog :one
+INSERT INTO core.email_log (project_id, template, to_email, subject, status, error)
+VALUES ($1, $2, $3, $4, $5, $6)
+RETURNING id, project_id, template, to_email, subject, status, error, created_at
+`
+
+type InsertEmailLogParams struct {
+	ProjectID pgtype.UUID `json:"project_id"`
+	Template  string      `json:"template"`
+	ToEmail   string      `json:"to_email"`
+	Subject   string      `json:"subject"`
+	Status    string      `json:"status"`
+	Error     string      `json:"error"`
+}
+
+func (q *Queries) InsertEmailLog(ctx context.Context, arg InsertEmailLogParams) (CoreEmailLog, error) {
+	row := q.db.QueryRow(ctx, insertEmailLog,
+		arg.ProjectID,
+		arg.Template,
+		arg.ToEmail,
+		arg.Subject,
+		arg.Status,
+		arg.Error,
+	)
+	var i CoreEmailLog
+	err := row.Scan(
+		&i.ID,
+		&i.ProjectID,
+		&i.Template,
+		&i.ToEmail,
+		&i.Subject,
+		&i.Status,
+		&i.Error,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
+const listEmailLog = `-- name: ListEmailLog :many
+SELECT id, project_id, template, to_email, subject, status, error, created_at FROM core.email_log
+WHERE project_id = $1
+ORDER BY created_at DESC
+LIMIT $2
+`
+
+type ListEmailLogParams struct {
+	ProjectID pgtype.UUID `json:"project_id"`
+	Limit     int32       `json:"limit"`
+}
+
+func (q *Queries) ListEmailLog(ctx context.Context, arg ListEmailLogParams) ([]CoreEmailLog, error) {
+	rows, err := q.db.Query(ctx, listEmailLog, arg.ProjectID, arg.Limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []CoreEmailLog
+	for rows.Next() {
+		var i CoreEmailLog
+		if err := rows.Scan(
+			&i.ID,
+			&i.ProjectID,
+			&i.Template,
+			&i.ToEmail,
+			&i.Subject,
+			&i.Status,
+			&i.Error,
+			&i.CreatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}