fix(workspace): keep the default Workspace path language-neutral

The first-use directory name and its stored title came from the Client's
startup language, so one product decision carried two incompatible
requirements: a path addressed by shell commands, tool arguments, @path
references, and session logs, and a label a reader reads.

The controller now owns the fixed `default-workspace` directory name and
the registry titles the Workspace after that same segment, so
`workspace.initializeDefault` takes no request at all —
WorkspaceInitializeDefaultRequest and its name validation are gone, and
the registry resolver returns a path instead of a path and title. No
language reaches the Host.

Browser consumers label a Workspace through the new
`workspaceDisplayTitle`: a title still equal to the automatic one reads
as the localized default name from the `common` namespace, every other
title reads verbatim. The Workspace browser resolves it once at the store
read, so rows, hover card, search meta, and the rename and delete dialogs
inherit it; the hero picker and the Conversation chip resolve it too.
Confirming a rename stores the text on screen, which is what stops a row
following the language.

packages/api/workspace-controller/package.json

@@ -26,6 +26,10 @@
       "types": "./lib/types/client/index.d.ts",
       "default": "./lib/client.js"
     },
+    "./default-workspace": {
+      "types": "./lib/types/default-workspace.d.ts",
+      "default": "./lib/types/default-workspace.js"
+    },
     "./typert": {
       "types": "./lib/typert.host.d.ts",
       "default": "./lib/typert.host.js"