Try every event database file on delete and say which was left (closes #275)

DeleteDB returned on the first event database file it failed to remove, so with WAL sidecars present a failure could be reported as "the file was left behind" after the events themselves were already gone. It now tries the database file and both sidecars, and its error says which case happened and names each file left: the database file is still on disk, or it is gone (the events are lost) and only a -wal or -shm sidecar remains. The webhook delete handler logs a different message for each and never says the events survive when they do not. Tests cover a normal delete with both sidecars, and a failed removal of the database file or a sidecar, through DeleteDB and the handler.

Model: opus-5-5

internal/handlers/export_test.go

@@ -36,6 +36,15 @@ const MaxRenderedAttemptsForTest = maxRenderedAttempts
 // the handlers enforce rather than a number copied beside it.
 const MaxTargetRetriesForTest = maxTargetRetries
 
+// EventDBLeftMsgForTest and SidecarLeftMsgForTest expose the two
+// messages the webhook delete handler logs when a file of the event
+// database is left on disk, so a test checking that one is absent
+// checks for the handler's own wording.
+const (
+	EventDBLeftMsgForTest = eventDBLeftMsg
+	SidecarLeftMsgForTest = sidecarLeftMsg
+)
+
 // PageOrFirstForTest exposes pageOrFirst for use in the handlers_test
 // package.
 func PageOrFirstForTest(s string) int {