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/src/api/workspace.schema.ts

@@ -31,14 +31,10 @@ export const workspaceListValueSchema = z.object({
   archivedSessionIds: z.array(sessionIdSchema),
 }) satisfies z.ZodType<Wire<ResponseValue<'workspace.list'>>>
 
-/** workspace.create request payload: exactly one of path/name (the contract's create spellings). */
+/** workspace.create request payload: the existing directory to adopt. */
 export const workspaceCreateRequestSchema = z.object({
-  path: z.string().optional(),
-  name: z.string().optional(),
-}).refine(
-  payload => (payload.path === undefined) !== (payload.name === undefined),
-  { message: 'workspace.create requires exactly one of path / name' },
-) satisfies z.ZodType<Wire<RequestPayload<'workspace.create'>>>
+  path: z.string(),
+}) satisfies z.ZodType<Wire<RequestPayload<'workspace.create'>>>
 
 /** workspace.create response value. */
 export const workspaceCreateValueSchema = z.object({