Add the loss-row banner class and retone degraded paste

02 ratified a warning-tone class for non-failure losses — content that
didn't arrive though nothing failed: a degraded paste, folders skipped
from a Finder drop, their future kin. Loss rows take the one-shot's
dismissable-untimed lifecycle (a loss the user didn't notice is the
harm) and rank below the true failures, above commit and attachment
notices. BannerCenter grows LossBanner, postLoss, and the
skipped-folders phrasing; the degraded-paste notice moves off its
signpost onto the new class, ending its too-quiet ranking.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/UI/BannerStripView.swift

@@ -245,6 +245,7 @@ private func previewError(
             .inProgress(InProgressOperation(label: "Pulling…")),
             .readOnlyLock(.vanishedRoot),
             .oneShot(OneShotBanner(error: previewError(.delete(title: "Ship the beta")))),
+            .loss(LossBanner(message: "Pasted 'Fix login' without its 3 attachments")),
             .historySuspended(HistorySuspension(reason: "the repository is corrupt")),
             .signpost(InfoSignpost(message: "This card changed on the remote — your edits still win")),
         ],
@@ -253,6 +254,19 @@ private func previewError(
     .frame(width: 520)
 }
 
+/// A loss row on its own: warning tone, but — unlike the standing `historySuspended` condition
+/// beside it in "Stacked tones" — dismissable, since a loss reports something that already
+/// happened rather than an ongoing state (settled 2026-07-28, BannerCenter's `LossBanner`).
+#Preview("Loss row") {
+    BannerStripView(
+        rows: [
+            .loss(LossBanner(message: BannerCenter.skippedFoldersMessage(count: 2))),
+        ],
+        onDismiss: { _ in }
+    )
+    .frame(width: 520)
+}
+
 /// Seven rows, one of them pinned: the strip shows the spinner plus the first three of the rest,
 /// and "+3 more" counts only what actually collapsed.
 #Preview("Collapse") {