feat(app): unify composer attachments with pill + lightbox redesign

Images and GitHub issues/PRs now live in one draft-store list (ComposerAttachment union) with cwd persisted on the draft. Paperclip becomes a + drop-up menu; queue button removed. Each pill uses a shared AttachmentPill wrapper with a corner-X that mirrors the auto-update toast spec. Pill body opens the attachment: GitHub via openExternalUrl, images via a new fullscreen AttachmentLightbox. GitHub picker auto-closes on select.

packages/app/src/contexts/session-context.tsx

@@ -53,6 +53,7 @@ import { derivePendingPermissionKey, normalizeAgentSnapshot } from "@/utils/agen
 import { resolveProjectPlacement } from "@/utils/project-placement";
 import { buildDraftStoreKey } from "@/stores/draft-keys";
 import type { AttachmentMetadata } from "@/attachments/types";
+import { splitComposerAttachmentsForSubmit } from "@/components/composer-attachments";
 import { reconcilePreviousAgentStatuses } from "@/contexts/session-status-tracking";
 import { patchWorkspaceScripts } from "@/contexts/session-workspace-scripts";
 import { isNative } from "@/constants/platform";
@@ -476,7 +477,13 @@ function SessionProviderInternal({ children, serverId, client }: SessionProvider
         if (queue && queue.length > 0) {
           const [next, ...rest] = queue;
           if (sendAgentMessageRef.current) {
-            void sendAgentMessageRef.current(agent.id, next.text, next.images);
+            const wirePayload = splitComposerAttachmentsForSubmit(next.attachments);
+            void sendAgentMessageRef.current(
+              agent.id,
+              next.text,
+              wirePayload.images,
+              wirePayload.attachments,
+            );
           }
           setQueuedMessages(serverId, (prev) => {
             const updated = new Map(prev);