feat(inbox): filter reports by signal source product

- Add source_product query param to SignalReportsQueryParams and API client
- Add sourceProductFilter to filter store (empty = all sources, persisted)
- Add "Source" multi-select section to toolbar filter/sort popover
- Pass source_product filter to API when any sources are selected
- Supports: session_replay, error_tracking, llm_analytics, github, linear, zendesk

Author: Twixes

apps/code/src/renderer/api/posthogClient.ts

@@ -953,6 +953,9 @@ export class PostHogAPIClient {
     if (params?.ordering) {
       url.searchParams.set("ordering", params.ordering);
     }
+    if (params?.source_product) {
+      url.searchParams.set("source_product", params.source_product);
+    }
 
     const response = await this.api.fetcher.fetch({
       method: "get",