feat(observability): phase 1 - schema, models & event log backend

Add database foundation for observability features:
- event_log table with severity/source filtering and pagination
- standalone_proxies table for user-created reverse proxies
- stale_threshold_days setting (default 7 days)
- Auto-persist warn/error events from event bus to database
- SSE broadcast of persistent events for real-time UI updates
- Frontend types and API functions for downstream UI phases

internal/store/standalone_proxy.go

@@ -0,0 +1,120 @@
+package store
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+
+	"github.com/google/uuid"
+)
+
+// CreateStandaloneProxy inserts a new standalone proxy record.
+func (s *Store) CreateStandaloneProxy(p StandaloneProxy) (StandaloneProxy, error) {
+	p.ID = uuid.New().String()
+	p.CreatedAt = Now()
+	p.UpdatedAt = p.CreatedAt
+
+	if p.HealthStatus == "" {
+		p.HealthStatus = "unknown"
+	}
+
+	_, err := s.db.Exec(
+		`INSERT INTO standalone_proxies (id, domain, destination_url, destination_port, ssl_certificate_id, npm_proxy_id, health_status, health_checked_at, created_at, updated_at)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		p.ID, p.Domain, p.DestinationURL, p.DestinationPort, p.SSLCertificateID,
+		p.NpmProxyID, p.HealthStatus, p.HealthCheckedAt, p.CreatedAt, p.UpdatedAt,
+	)
+	if err != nil {
+		return StandaloneProxy{}, fmt.Errorf("insert standalone proxy: %w", err)
+	}
+	return p, nil
+}
+
+// GetStandaloneProxy returns a standalone proxy by ID.
+func (s *Store) GetStandaloneProxy(id string) (StandaloneProxy, error) {
+	var p StandaloneProxy
+	err := s.db.QueryRow(
+		`SELECT id, domain, destination_url, destination_port, ssl_certificate_id, npm_proxy_id, health_status, health_checked_at, created_at, updated_at
+		 FROM standalone_proxies WHERE id = ?`, id,
+	).Scan(&p.ID, &p.Domain, &p.DestinationURL, &p.DestinationPort, &p.SSLCertificateID,
+		&p.NpmProxyID, &p.HealthStatus, &p.HealthCheckedAt, &p.CreatedAt, &p.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return StandaloneProxy{}, fmt.Errorf("standalone proxy %s: %w", id, ErrNotFound)
+	}
+	if err != nil {
+		return StandaloneProxy{}, fmt.Errorf("query standalone proxy: %w", err)
+	}
+	return p, nil
+}
+
+// ListStandaloneProxies returns all standalone proxy records ordered by creation time.
+func (s *Store) ListStandaloneProxies() ([]StandaloneProxy, error) {
+	rows, err := s.db.Query(
+		`SELECT id, domain, destination_url, destination_port, ssl_certificate_id, npm_proxy_id, health_status, health_checked_at, created_at, updated_at
+		 FROM standalone_proxies ORDER BY created_at DESC`,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("query standalone proxies: %w", err)
+	}
+	defer rows.Close()
+
+	proxies := []StandaloneProxy{}
+	for rows.Next() {
+		var p StandaloneProxy
+		if err := rows.Scan(&p.ID, &p.Domain, &p.DestinationURL, &p.DestinationPort, &p.SSLCertificateID,
+			&p.NpmProxyID, &p.HealthStatus, &p.HealthCheckedAt, &p.CreatedAt, &p.UpdatedAt); err != nil {
+			return nil, fmt.Errorf("scan standalone proxy: %w", err)
+		}
+		proxies = append(proxies, p)
+	}
+	return proxies, rows.Err()
+}
+
+// UpdateStandaloneProxy updates an existing standalone proxy's mutable fields.
+func (s *Store) UpdateStandaloneProxy(p StandaloneProxy) error {
+	p.UpdatedAt = Now()
+	result, err := s.db.Exec(
+		`UPDATE standalone_proxies SET domain=?, destination_url=?, destination_port=?, ssl_certificate_id=?, npm_proxy_id=?, health_status=?, health_checked_at=?, updated_at=?
+		 WHERE id=?`,
+		p.Domain, p.DestinationURL, p.DestinationPort, p.SSLCertificateID,
+		p.NpmProxyID, p.HealthStatus, p.HealthCheckedAt, p.UpdatedAt, p.ID,
+	)
+	if err != nil {
+		return fmt.Errorf("update standalone proxy: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("standalone proxy %s: %w", p.ID, ErrNotFound)
+	}
+	return nil
+}
+
+// DeleteStandaloneProxy removes a standalone proxy by ID.
+func (s *Store) DeleteStandaloneProxy(id string) error {
+	result, err := s.db.Exec(`DELETE FROM standalone_proxies WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("delete standalone proxy: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("standalone proxy %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
+// UpdateProxyHealth updates the health status and check timestamp for a standalone proxy.
+func (s *Store) UpdateProxyHealth(id string, status string) error {
+	ts := Now()
+	result, err := s.db.Exec(
+		`UPDATE standalone_proxies SET health_status=?, health_checked_at=?, updated_at=? WHERE id=?`,
+		status, ts, ts, id,
+	)
+	if err != nil {
+		return fmt.Errorf("update proxy health: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("standalone proxy %s: %w", id, ErrNotFound)
+	}
+	return nil
+}