Track inbound filters by error message usage and impact

### Problem Statement

When the list of inbound filters grows large, users can't determine which ones to remove because there's no visibility into which filters are actually affecting events, how many events each filter is blocking or which filters are still relevant versus stale

### Solution Brainstorm

Add metrics to each inbound filter showing the number of events blocked per day/week/month, the last time the filter was triggered and a visual indicator of filter activity level

### Product Area

Ingestion and Filtering

The issue identifies the Ingestion and Filtering product area but names no files, tests, or entry points. Start by locating the inbound-filter model and its event-processing and UI entry points. Done means each filter exposes blocked-event counts over time, its last trigger time, and an activity indicator.

Written by the indexing model from the issue text.