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/api-proxy-approval.spec.ts

@@ -27,7 +27,7 @@ async function harness(): Promise<{ ctx: Context; api: ApiProxy }> {
   await ctx.plugin(UserInteractionService)
   await ctx.plugin(AgentRegistry)
   await ctx.plugin(ApprovalService)
-  const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp', workspaceRoot: '/tmp' })
+  const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp' })
   return { ctx, api }
 }
 
@@ -217,7 +217,7 @@ describe('approval pending registry', () => {
     await ctx.plugin(ApprovalService)
     let api!: ApiProxy
     const fiber = ctx.plugin(Object.assign((fiberCtx: Context) => {
-      api = createApiProxy(fiberCtx, { provider: 'p', model: 'm', cwd: '/tmp', workspaceRoot: '/tmp' })
+      api = createApiProxy(fiberCtx, { provider: 'p', model: 'm', cwd: '/tmp' })
     }, { inject: ['sessions', 'agents', 'userInteraction', 'approval'] }))
     await fiber.await()
     const abort = new AbortController()