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/todo/tool-todo/tests/projection.spec.ts

@@ -45,7 +45,7 @@ async function harness(withTodoTool: boolean): Promise<Bench> {
   if (withTodoTool) await ctx.plugin(ToolTodo, { allowParallelInProgress: true })
   const session = ctx.sessions.create()
   ctx.agents.register({ id: session.id, session, status: 'idle', ctx } as Agent)
-  const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp', workspaceRoot: '/tmp' })
+  const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp' })
   return {
     ctx,
     session,