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/client/connection/src/client/fixture.ts

@@ -2122,15 +2122,14 @@ export function createFixtureApi(options: FixtureOptions = {}): ApiProxy {
         archivedSessionIds: [...archivedSessionIds],
       }),
       create: (request) => {
-        const { path, name } = request.payload
-        const target = path ?? `/tmp/fixture-workspaces/${name ?? ''}`
-        const existing = workspaces.find(w => w.path === target)
+        const { path } = request.payload
+        const existing = workspaces.find(w => w.path === path)
         if (existing !== undefined) return ok(request, { workspace: { ...existing }, created: false })
         const now = new Date().toISOString()
         const created: WorkspaceView = {
           workspaceId: wid(`fx-ws-${nextWorkspace++}`),
-          path: target,
-          title: name ?? target.split('/').filter(Boolean).at(-1) ?? target,
+          path,
+          title: path.split('/').filter(Boolean).at(-1) ?? path,
           sessionIds: [],
           createdAt: now,
           updatedAt: now,