app: rename the System map route /map -> /system

The nav label was already "System" and the page is SystemMap; only the URL
was stale. Move it to /system, add a back-compat redirect from /map, and update
the command-palette navigations. Unrelated graph node type "map" left as-is.

app/src/pages/SystemMap.tsx

@@ -987,7 +987,7 @@ export function SystemMapPage() {
     setFocus(picks.length === 1 ? picks[0].id : null)
   }, [])
 
-  // "Go to on map" from the command palette (/map?focus=<id>): select + center it.
+  // "Go to on map" from the command palette (/system?focus=<id>): select + center it.
   useEffect(() => {
     const f = searchParams.get("focus")
     if (!f) return