feat(queue): queue a message with everything the composer had attached

Queueing captured only the text and files. Context chips (inline comments,
terminal selections, browser annotations, PR comments and checks, quotes,
linked issue/PR/Linear references, pending synthetic parts) stayed in the
composer and only left with the next manual send, so a queued message the
server delivered went out without them and the chips rode an unrelated
message later.

A queued message now carries what the composer would have sent: the text
with its agent mention stripped and file mentions resolved into
attachments, the attached context as structured parts, and the skill
instruction derived from the text. The server delivers those parts in the
composer's order, the VS Code auto-send does the same, and editing a queued
message puts the chips and linked references back. A failed queue restores
the composer completely. Snapshots and broadcasts omit the captured
context like attachment payloads; a take returns it.

Claude-Session: https://claude.ai/code/session_01HB9wdLQoZX2vfyDjwv6Rso

packages/ui/src/components/chat/composer/DOCUMENTATION.md

@@ -159,8 +159,14 @@ and the send path reading the same grammar.
   linked issue/PR) becomes its own synthetic text part carrying structured
   metadata** built by `lib/messages/contextParts.ts`; the timeline reads that
   metadata back to render context blocks. PR instructions precede the PR diff.
-  Queueing a message leaves context drafts in their store on purpose — the send
-  that later delivers the queue consumes them.
+  The same module's `buildComposerContext` captures that context when a message
+  is **queued** instead of sent: the chips leave the composer with the message
+  (as `QueuedContextPart`s on the queue item), the server or the VS Code
+  auto-send delivers them through `queuedContextToParts`, and editing the
+  queued message puts them back. A queued message is placed as captured — its
+  mention, file mentions, and skill instruction were resolved when it was
+  queued, never at delivery — and its context follows it before the next
+  queued message.
 - `state/useComposerDraft.ts` — a draft belongs to a (runtime, directory,
   session) identity. Writes are debounced while typing but forced at every edge
   where the page may stop running, because a pending timer is not a saved