feat(runtimes): add usage charts, activity heatmap, and hourly distribution

Add comprehensive data visualization to the runtime detail page:
- Daily token usage stacked area chart and daily cost bar chart
- Model distribution donut chart with cost breakdown
- GitHub-style activity heatmap (13 weeks of daily token usage)
- Hourly task distribution bar chart with new backend endpoint
- Responsive 2-column grid layout for charts on wide screens

Backend: new GET /api/runtimes/{runtimeId}/activity endpoint
returning hourly task counts from agent_task_queue.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/pkg/db/generated/runtime_usage.sql.go

@@ -11,6 +11,39 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
+const getRuntimeTaskHourlyActivity = `-- name: GetRuntimeTaskHourlyActivity :many
+SELECT EXTRACT(HOUR FROM started_at)::int AS hour, COUNT(*)::int AS count
+FROM agent_task_queue
+WHERE runtime_id = $1 AND started_at IS NOT NULL
+GROUP BY hour
+ORDER BY hour
+`
+
+type GetRuntimeTaskHourlyActivityRow struct {
+	Hour  int32 `json:"hour"`
+	Count int32 `json:"count"`
+}
+
+func (q *Queries) GetRuntimeTaskHourlyActivity(ctx context.Context, runtimeID pgtype.UUID) ([]GetRuntimeTaskHourlyActivityRow, error) {
+	rows, err := q.db.Query(ctx, getRuntimeTaskHourlyActivity, runtimeID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []GetRuntimeTaskHourlyActivityRow{}
+	for rows.Next() {
+		var i GetRuntimeTaskHourlyActivityRow
+		if err := rows.Scan(&i.Hour, &i.Count); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const getRuntimeUsageSummary = `-- name: GetRuntimeUsageSummary :many
 SELECT provider, model,
     SUM(input_tokens)::bigint AS total_input_tokens,