feat(app): make search N-ary, with multi-source as the default shape

.changeset/multi-source-filters.md

@@ -0,0 +1,10 @@
+---
+'@hyperdx/app': minor
+---
+
+The filters sidebar now works when searching multiple sources. Facet fields
+and values merge across the selected sources, and checking a value filters
+every source that has the field. A source whose table lacks a filtered column
+is excluded from the results with a visible reason on its status chip instead
+of silently returning unfiltered rows. Filter pills and add-to-filter from the
+row side panel work in multi-source mode too.

.changeset/multi-source-search.md

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+---
+'@hyperdx/app': minor
+'@hyperdx/common-utils': minor
+---
+
+Search across multiple sources at once. The search page's source selector can
+now expand into a multi-select (up to 3 log/trace sources): results interleave
+into one timestamp-ordered timeline with a per-row source badge, normalized
+columns (Timestamp, Source, Service, Level, Message, and Duration when traces
+are included), a histogram stacked by source, and an add-column picker over the
+union of the selected sources' columns. Each source runs its own query
+pipeline — sources on different connections work, and a failing source shows a
+status chip instead of failing the whole search. Multi-source mode is
+Lucene-only and shareable via URL; saved searches and alerts remain
+single-source for now.