Name what failed in a repository check from its whole output, not its tail (issue 460)

A long run's logs pushed the --- FAIL lines out of the last 200 lines the
summary was named from, so a failed check could not say which test failed.
Pick the lines that name a failure as the output streams, keep them whole at
the end of the verdict's report, and say the whole output in the build's log.

internal/builder/testdata/issue460/CAPTURED

@@ -0,0 +1,7 @@
+Captured 2026-10-11 from real `go test` runs (go1.27.1, linux/amd64) of a throwaway module whose
+packages fail each way a repository's own check fails: a test failing early in a run its own logs
+then fill (early: 600 log lines after the failures), a panic, a data race under -race, a build error,
+and one -race run of every package. Only the module's directory was rewritten to /src/cap.
+
+They are the output shapes of novox/hq issue 460: mesh-controller #218's check printed its
+`--- FAIL:` line before the store-backed package's logs, which pushed it out of the report's tail.