fix(channel-monitor-v2): clear CI lint and align trend axis with range zoom

Fix golangci unused/gofmt on the gentle-backfill path. Plot matrix and
line-chart X axes on the selected [requested_start, requested_end)
window (empty slots while backfill lags), and let plain mouse-wheel zoom
narrow the visible interval so pulse blocks grow wider.

frontend/src/api/channelMonitorV2.ts

@@ -86,6 +86,8 @@ export interface MonitorBootstrap {
 
 export interface MonitorCoverage {
   requested_start: string
+  /** Exclusive upper bound of the UI-selected range (filter end). */
+  requested_end?: string
   coverage_start: string
   data_through: string
   computed_at: string