fix(app): source composer cwd from agent state, not draft hook

The GitHub picker showed "No results found." for any running agent after
the first message was sent. useAgentInputDraft owned a local cwd state
that clear("sent") wiped to "", so the composer read cwd: "" even though
the agent's real cwd was correct on the wire.

Drop cwd ownership from the hook. Composer takes cwd as a prop sourced
by the parent — agentState.cwd for running agents, composerState.workingDir
for drafts, sourceDirectory for setup flows. The hook now persists only
{text, attachments}. Legacy persisted drafts with a cwd field still
hydrate; tagged COMPAT(draft-cwd) for removal after 2026-11-09.

Also moves attachment pills back inside the composer's bordered surface
via a new attachmentSlot prop on MessageInput, and shrinks pill height
from 48 to 32 — the subagents-track tuck previously had attachments
floating between it and the input.

Adds one Playwright spec asserting the draft-create-agent path submits
the workspace cwd.

packages/app/src/components/workspace-setup-dialog.tsx

@@ -151,7 +151,6 @@ export function WorkspaceSetupDialog() {
   const isConnected = useHostRuntimeIsConnected(serverId);
   const chatDraft = useAgentInputDraft({
     draftKey: `workspace-setup:${serverId}:${sourceDirectory}`,
-    initialCwd: sourceDirectory,
     composer: buildChatDraftComposerArgs({
       serverId,
       isConnected,
@@ -393,7 +392,7 @@ export function WorkspaceSetupDialog() {
           onChangeText={chatDraft.setText}
           attachments={chatDraft.attachments}
           onChangeAttachments={chatDraft.setAttachments}
-          cwd={chatDraft.cwd}
+          cwd={sourceDirectory}
           clearDraft={chatDraft.clear}
           autoFocus
           commandDraftConfig={composerState?.commandDraftConfig}