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/utils/assetUrls.ts

@@ -1,4 +1,4 @@
-import { getApiForOrigin } from '../stores/serverStore';
+import { getApiForOrigin } from '../stores/spaceStore';
 
 /**
  * Resolve a relative asset filename to an absolute URL for remote origins.