refactor: rename Server → Space across entire codebase

Renames all domain terminology from "Server" to "Space" throughout the
application — database schema, API routes, shared types, stores, components,
and UI strings. Files renamed: ServerSidebar → SpaceSidebar, CreateServer →
CreateSpace, JoinServer → JoinSpace, ServerSettings → SpaceSettings,
serverStore → spaceStore, routes/servers → routes/spaces.

packages/web/src/App.tsx

@@ -37,7 +37,7 @@ export function App() {
         }
       />
       <Route
-        path="/channels/:serverId/:channelId?"
+        path="/channels/:spaceId/:channelId?"
         element={
           <ProtectedRoute>
             <AppLayout />