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/screens/workspace/workspace-draft-agent-tab.tsx

@@ -310,7 +310,6 @@ export function WorkspaceDraftAgentTab({
   );
   const draftInput = useAgentInputDraft({
     draftKey: draftStoreKey,
-    initialCwd: workspaceDirectory ?? "",
     composer: {
       initialServerId: serverId,
       initialValues: workspaceDirectory ? { workingDir: workspaceDirectory } : undefined,
@@ -338,7 +337,7 @@ export function WorkspaceDraftAgentTab({
   const isCompact = useIsCompactFormFactor();
   const workspaceAttachmentScopeKey = useWorkspaceAttachmentScopeKey({
     serverId,
-    cwd: draftInput.cwd,
+    cwd: composerState.workingDir,
     workspaceId,
   });
   const workspaceAttachments = useWorkspaceAttachments(workspaceAttachmentScopeKey);
@@ -613,7 +612,7 @@ export function WorkspaceDraftAgentTab({
             workspaceAttachments={workspaceAttachments}
             onOpenWorkspaceAttachment={handleOpenWorkspaceAttachment}
             onChangeAttachments={draftInput.setAttachments}
-            cwd={draftInput.cwd}
+            cwd={composerState.workingDir}
             clearDraft={draftInput.clear}
             autoFocus={shouldAutoFocusWorkspaceDraftComposer({ isPaneFocused, isSubmitting })}
             onAddImages={handleAddImagesCallback}