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-models.spec.ts

@@ -125,7 +125,7 @@ describe('Web session model selection', () => {
       model: 'private-preview',
       reasoningEffort: ReasoningEffortId('max'),
     })
-    const api = createApiProxy(ctx, { provider: 'deepseek-official', model: 'deepseek-chat', cwd: '/tmp', workspaceRoot: '/tmp' })
+    const api = createApiProxy(ctx, { provider: 'deepseek-official', model: 'deepseek-chat', cwd: '/tmp' })
 
     const catalog = expectValue(await api.sessions.models(request({ sessionId })))
     expect(catalog.current).toEqual({
@@ -160,7 +160,7 @@ describe('Web session model selection', () => {
 
   it('accepts an advisory-unlisted model, rejects an unavailable provider, and switches only after the next assembly', async () => {
     const { ctx, agent, sessionId } = await harness()
-    const api = createApiProxy(ctx, { provider: 'deepseek-official', model: 'deepseek-chat', cwd: '/tmp', workspaceRoot: '/tmp' })
+    const api = createApiProxy(ctx, { provider: 'deepseek-official', model: 'deepseek-chat', cwd: '/tmp' })
     const seed: LlmCallConfig = { provider: 'seed', model: 'seed', temperature: 0.2 }
     const signal = new AbortController().signal