feat(diagnostics): walk the log lines from the keyboard; name the console "Server log"

Both log viewers put their lines in a NavGrid: j/k (and the arrows) step
from line to line, and Enter opens one exactly as a click does (the line's
button is its `data-nav-open`). A focused line is named by its code and
message.

The console's nav entry is "Szervernapló" / "Server log", its page title:
"Diagnosztika" was already the Settings tab that holds the user's own log,
and two places with one name read as one place.

frontend/src/components/LogLine.tsx

@@ -1,10 +1,12 @@
 import type { ReactNode } from "react";
 
 import type { Level } from "../lib/log";
+import { navItemAttrs } from "../lib/listNav";
 
 // One log line as both log viewers draw it — "Saját napló" (this tab's ring) and the admin
 // diagnostics console (the server's stored log): time, level, event code, message, and the line opens
 // in place to whatever detail its screen has. One component, so a level reads the same on both.
+// Inside a NavGrid the keyboard walks the lines (`j`/`k`) and Enter opens one, as a click does.
 
 const LEVEL_TAG: Record<Level, { text: string; className: string }> = {
   TRACE: { text: "TRACE", className: "text-muted opacity-80" },
@@ -30,6 +32,7 @@ export default function LogLine({
   open,
   onToggle,
   title,
+  navIndex,
   children,
 }: {
   ts: string;
@@ -40,14 +43,20 @@ export default function LogLine({
   onToggle: () => void;
   /** The row button's tooltip — the admin console puts the full date there. */
   title?: string;
+  /** The line's place in its NavGrid. */
+  navIndex: number;
   /** The detail shown while the line is open. */
   children: ReactNode;
 }) {
   const tag = LEVEL_TAG[level];
   return (
-    <div className="border-b border-border/50 last:border-b-0">
+    <div
+      className="border-b border-border/50 last:border-b-0"
+      {...navItemAttrs(navIndex, `${event} ${msg}`)}
+    >
       <button
         type="button"
+        data-nav-open
         aria-expanded={open}
         onClick={onToggle}
         title={title}