feat(host): directory-picker capability seam with dialog and browse backends

The web GUI's folder picking was hardwired to one interaction: a native
OS chooser compiled into the gateway, unusable for remote deployments
and swappable only by editing apiproxy source.

Directory picking becomes a three-package capability seam in
packages/host: ctx.directoryPicker returns a discriminated capability —
dialog (the extracted native chooser; host-display only) or browse
(new: one-level listing + child creation over Node stdlib, hidden flags
host-stamped, symlinks followed, ancestry crumbs; remote-capable). The
gateway injects the seam, advertises the kind via
host.describe.directoryPicker, serves host.listDirectory /
host.createDirectory under browse, and answers
directory-picker-unavailable across kinds. cordis.yml is the swap
point; apps/cli keeps dialog mounted, so behavior is unchanged until
the in-app browser PR flips the default. The connection fixture serves
a deterministic browse tree; WorkspacesService gains the browse calls
the browser UI will drive. Decision record:
.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md

tsconfig.host.json

@@ -163,6 +163,9 @@
     { "path": "./packages/hooks/hooks-codex" },
     { "path": "./packages/mcp/mcp-client" },
     { "path": "./packages/host/apiproxy" },
+    { "path": "./packages/host/directory-picker" },
+    { "path": "./packages/host/directory-picker-browse" },
+    { "path": "./packages/host/directory-picker-dialog" },
     { "path": "./packages/host/webserver" },
     { "path": "./packages/sdk/sdk-client" },
     { "path": "./packages/sdk/helper" },