feat(nav): each module declares its URL keys; a page switch clears them and a page opens without another's

The shell cleared a hand-kept key list on a page switch (it missed the Files and feed keys) and cleared
nothing when a page opened from a link carrying another page's keys. ModuleDef.urlKeys now names every
key a page's view writes, the shell derives both from the registry, and moduleUrl.contract.test holds the
declarations true: one owner per key, no shell key, exactly what each codec writes, and no undeclared
key literal in the app.

frontend/src/lib/moduleDef.ts

@@ -44,4 +44,10 @@ export type ModuleDef = {
   // Static, unlike the page: it is on the boot path by design. It reads no other module's store, so
   // the order the stores nest in does not matter (moduleStores.contract.test).
   Store?: ComponentType<{ children: ReactNode }>;
+  // Every address-bar key this page's view writes: its filters, sort, tab, the item it shows. The URL
+  // IS the view, so a bookmark reopens it. The shell clears them all on a page switch, and opens a page
+  // with no other page's keys in its address (NavigationProvider), so one page's state never rides
+  // along onto another's URL. Empty for a page with nothing of its own in the URL. Each key belongs to
+  // one module and none is a shell key (moduleUrl.contract.test).
+  urlKeys: readonly string[];
 };