fix(host): bound listDirectory levels at a configurable maxEntries

One list call now materializes at most maxEntries child rows (config,
default 1000 - GitHub's web-UI directory-listing bound). Candidates sort
before probing so a cut level keeps the name-sorted head and symlink
probing stops with the bound, and DirectoryListing carries a required
truncated flag on the seam and the wire so clients can state
incompleteness instead of silently missing tail entries.

packages/host/apiproxy/tests/api-proxy-workspace.spec.ts

@@ -159,6 +159,7 @@ const BROWSE_STUB: DirectoryPickerCapability = {
       home: '/home/user',
       crumbs: [{ name: '/', path: '/', hidden: false }],
       entries: [{ name: 'projects', path: `${target}/projects`, hidden: false }],
+      truncated: false,
     }
   },
   createDirectory: async (path, name) => {