feat(webui): add project workspaces and access controls (#4007)

* feat(webui): add project workspaces and access controls

* feat(webui): add project workspaces and access controls

* refactor(tools): centralize workspace access resolution

* refactor(webui): remove unused workspace host state

* fix(webui): hide estimated file edit label

* fix(webui): clarify file edit deletion feedback

* fix(webui): label deleted file activity

* fix(webui): flatten file edit activity rows

* fix(core): remove path-only patch deletion

* fix(core): keep apply patch non-destructive

* refactor(webui): trim workspace host plumbing

* fix(tools): register exec with tools config

webui/src/components/thread/ThreadViewport.tsx

@@ -271,9 +271,11 @@ export function ThreadViewport({
           </div>
         ) : (
           <div ref={contentRef} className="mx-auto flex min-h-full w-full max-w-[72rem] flex-col px-4">
-            <div className="flex w-full flex-1 items-center justify-center pb-[7vh] pt-8">
-              <div className="flex w-full max-w-[58rem] flex-col gap-6">
-                {emptyState}
+            <div className="flex w-full flex-1 items-center justify-center py-10 sm:py-12">
+              <div className="relative w-full max-w-[58rem]">
+                <div className="absolute inset-x-0 bottom-[calc(100%+1.5rem)] flex justify-center">
+                  {emptyState}
+                </div>
                 <div className="w-full">{composer}</div>
               </div>
             </div>