refactor: drop the create-by-name workspace route

The Web picker collapsed onto the directory flow (see the one-route-to-add-a-workspace
Agent Note), leaving workspace.create({ name }) with no product consumer. Delete the
whole feed line: the wire schema's name member and WorkspaceApi spelling, the gateway's
workspaceRoot config/default and the mkdir branch, the client seam that carried the name
(WorkspaceCreateInput, WorkspacesService.create, intentName), the dsh web
--workspace-root flag, and the fixture's name handling. workspace-name-conflict stays as
workspace.rename's duplicate-title error.

packages/host/apiproxy/tests/client-handler.spec.ts

@@ -378,8 +378,8 @@ describe('workspace domain round trip', () => {
     expect(archivedResponse.result).toEqual({ ok: true, value: { archivedSessionIds: ['s-arch'] } })
   })
 
-  it('rejects a create payload violating the exactly-one refine at the handler', async () => {
-    const response = await client(scriptedApi()).workspace.create({})
+  it('rejects a pathless create payload at the handler schema', async () => {
+    const response = await client(scriptedApi()).workspace.create({} as never)
     expect(response.result.ok).toBe(false)
     if (!response.result.ok) expect(response.result.error.code).toBe('bad-request')
   })