refactor(runtimes): split monolithic page, add zustand store, time range selector, and delete support

- Split 1189-line runtimes-page.tsx into focused sub-components (list, detail, ping, usage, 5 chart files, shared UI, utils)
- Add useRuntimeStore zustand store for shared runtime state across pages (agents page now uses it too)
- Add 7d/30d/90d time range selector to usage charts
- Add full-stack runtime delete: SQL query, Go handler, API route, frontend with confirmation dialog
- Remove unused daemon:heartbeat WS listener (server never broadcasts it)

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

@@ -11,6 +11,21 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
+const deleteAgentRuntime = `-- name: DeleteAgentRuntime :exec
+DELETE FROM agent_runtime
+WHERE id = $1 AND workspace_id = $2
+`
+
+type DeleteAgentRuntimeParams struct {
+	ID          pgtype.UUID `json:"id"`
+	WorkspaceID pgtype.UUID `json:"workspace_id"`
+}
+
+func (q *Queries) DeleteAgentRuntime(ctx context.Context, arg DeleteAgentRuntimeParams) error {
+	_, err := q.db.Exec(ctx, deleteAgentRuntime, arg.ID, arg.WorkspaceID)
+	return err
+}
+
 const getAgentRuntime = `-- name: GetAgentRuntime :one
 SELECT id, workspace_id, daemon_id, name, runtime_mode, provider, status, device_info, metadata, last_seen_at, created_at, updated_at FROM agent_runtime
 WHERE id = $1