feat(nav): slim hover-expand sidebar, role tooltip, logout button

The rail now sits slim by default and expands to a labelled overlay on hover
or keyboard focus without pushing content; the manual toggle became a pin
(pinned = the old in-flow expanded rail). The header no longer reserves a fixed
504px left offset — it's absolutely positioned inside the content column, so it
tracks the actual left zone and reclaims the dead gap. The role badge is gone;
role now shows via a title tooltip on the username, and a logout quick-button
joins the language/about cluster.

frontend/src/i18n/locales/en/nav.json

@@ -1,7 +1,7 @@
 {
   "primary": "Primary navigation",
-  "collapse": "Collapse sidebar",
-  "expand": "Expand sidebar",
+  "pin": "Pin sidebar open",
+  "unpin": "Unpin sidebar",
   "adminSection": "Admin",
   "role": {
     "admin": "Admin",

frontend/src/i18n/locales/hu/nav.json

@@ -1,7 +1,7 @@
 {
   "primary": "Fő navigáció",
-  "collapse": "Oldalsáv összecsukása",
-  "expand": "Oldalsáv kinyitása",
+  "pin": "Oldalsáv rögzítése nyitva",
+  "unpin": "Oldalsáv rögzítésének feloldása",
   "adminSection": "Admin",
   "role": {
     "admin": "Admin",