feat(app): support SQL search across sources, and say when one is excluded

.changeset/multi-source-filters.md

@@ -0,0 +1,12 @@
+---
+'@hyperdx/app': minor
+---
+
+The filters sidebar works across every selected source. Facet fields and
+values merge across sources, value counts are summed, "load more" fans out,
+and pins (personal and team-shared) read as a union and apply to the whole
+selection. 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 across
+sources 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.

.changeset/multi-source-select-builder.md

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+---
+'@hyperdx/common-utils': minor
+---
+
+Add a builder for search queries that project a canonical, source-independent
+column set. Given a source, it emits that source's semantic expressions
+(timestamp, service, severity/status, body/span name, duration) under shared
+aliases, and pads columns a source doesn't have with NULL, so results from
+different tables share one shape.

.changeset/multi-source-sql-and-exclusion.md

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+---
+'@hyperdx/app': minor
+'@hyperdx/common-utils': minor
+---
+
+SQL search now works across multiple sources, and a source that can't answer
+the search says so. Previously multi-source search refused SQL outright, and a
+Lucene query naming a field a source doesn't have silently returned nothing
+from that source — the field resolved to a condition matching no rows. Both
+languages now resolve the columns a search references against each source's
+schema up front: sources that have them run the query, and a source that
+doesn't is excluded with the missing column named on its status chip.

.changeset/null-literal-select-alias.md

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+---
+'@hyperdx/common-utils': patch
+---
+
+Fix `NULL AS "alias"` projections being dropped from the SELECT alias map. A
+column projected as a NULL literal was omitted, so anything resolving a value
+back to its source expression (for example building a WHERE clause that
+identifies a specific row) treated the alias as a real table column and
+produced SQL referencing a column that does not exist.