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/test-runtime/tests/runtime.spec.tsx

@@ -559,8 +559,8 @@ describe('workspaces action face', () => {
   it('records every IWorkspaces verb with inert defaults and honors stubs', async () => {
     const runtime = await SlotTestRuntime.create()
     const ws = runtime.workspaces
-    const created = await ws.create({ name: 'alpha' })
-    expect(created.title).toBe('alpha')
+    const created = await ws.create({ path: '/tmp/alpha' })
+    expect(created.title).toBe('/tmp/alpha')
     const registered = await ws.create({ path: '/tmp/beta' })
     expect(registered.path).toBe('/tmp/beta')
     await expect(ws.pickDirectory()).resolves.toBeNull()
@@ -584,7 +584,7 @@ describe('workspaces action face', () => {
     ws.stub('openPath', () => Promise.resolve())
     ws.stub('insertSessionBefore', () => Promise.resolve({ workspaceId: 'w1', title: '', path: '', sessionIds: [] } as never))
     ws.stub('archiveSession', () => Promise.resolve())
-    expect((await ws.create({ name: 'y' })).title).toBe('X')
+    expect((await ws.create({ path: '/y' })).title).toBe('X')
     await expect(ws.pickDirectory()).resolves.toBe('/picked')
     expect((await ws.rename('w1' as WorkspaceId, 'z')).title).toBe('S')
     await ws.delete('w1' as WorkspaceId)