fix(client): let page descriptions hold one line

PageHeader capped its description at maxWidth: 640, which wraps every
page description well before the text runs out - the uptime one is 100
characters and needs roughly 700px at 14px.

Now 108ch, sized against the longest description in en.json (113 chars,
the notifications page). Still a cap, so the line wraps on narrow
viewports and does not run the full width of a large display, and `ch`
tracks the font size rather than assuming 14px forever.

The empty-state description keeps its 360px cap - that copy is centred
and reads better narrow.

Claude-Session: https://claude.ai/code/session_01AbYLvwpEaZFXktHVcqrFRd

client/src/Components/design-elements/PageHeader.tsx

@@ -109,7 +109,10 @@ export const PageHeader = ({
 							fontSize: 14,
 							color: theme.palette.text.secondary,
 							lineHeight: 1.55,
-							maxWidth: 640,
+							// Wide enough to hold a one-line page description at this
+							// size; still a cap, so it wraps rather than running the
+							// full width of a large monitor.
+							maxWidth: "108ch",
 						}}
 					>
 						{description}