feat(ui): E31 S4a — rail rows are links, the channel page opens on unwatched, users and audit tidied

- Nav rail page rows are real links (/?page=<id>): a middle-click or
  Ctrl-click opens the page in a new tab; a plain click stays in-app.
- A fresh channel page shows the unwatched videos; a picked watch state
  is a remembered preference (channelShow).
- Users: the role, suspend and delete move into the row's one menu
  (the "…", right-click, Shift+F10); locked ones keep their reason.
- Audit log: back-to-back successful runs of one job fold into one row
  that opens to the earlier ones; a failed run reads in the danger colour.
- DESIGN.md decision log: the E31 picks.

frontend/src/components/ui/pressableSelectable.contract.test.ts

@@ -46,7 +46,7 @@ const PLAIN: Record<string, [number, string]> = {
   "ui/ActionMenu.tsx": [1, "a menu row"],
   "ui/BackToTop.tsx": [1, "a control"],
   "ui/CommandPalette.tsx": [1, "a command row"],
-  "ui/NavRail.tsx": [2, "nav items"],
+  "ui/NavRail.tsx": [1, "the action rows (About, Sign out); a page row is a link (E31)"],
   "ui/PanelGroup.tsx": [2, "a group's collapse toggle and its label"],
   "ui/SidePanel.tsx": [2, "panel controls"],
   "ui/tableHeader.tsx": [1, "a column's sort header"],