fix(chat): restore file attachments when reverting or forking messages (#1288)

* chore: add .worktrees/ to gitignore for worktree workflow

* fix(chat): restore file attachments when reverting or forking messages

* fix(chat): address review findings in attachment restoration

- Move filePartsToAttachments helper below all imports into its own
  'Attachment helpers' section (was incorrectly placed between imports)
- Compute size from base64 data URL for pasted screenshots instead of
  hardcoding 0; file:// URLs keep size 0 which formatFileSize suppresses
  gracefully
- Capture prevAttachedFiles before optimistic mutation and restore on
  SDK revert failure
- Always use source: 'local' for restored attachments so they are
  visible and removable in the composer regardless of URL scheme

* fix(chat): resolve merge conflicts and restore attachments in fork

- Merge upstream main which already added attachment restoration to
  revertToMessage via addRestoredAttachment
- Add !isSyntheticPart filter to revertToMessage file part collection
  (upstream was missing this)
- Add attachment restoration to forkFromMessage (was not fixed upstream)
- Use upstream's addRestoredAttachment approach for consistency

* fix(chat): clear restored attachments when opening new session draft

Reverted-message attachments (and any other pending attachments in the
global input store) were carrying over to the new session input because
openNewSessionDraft did not clear attachedFiles.

Clear attachedFiles in openNewSessionDraft, which is the navigation-away
event for new sessions (it already sets currentSessionId: null). This
matches the semantics of starting a fresh conversation.

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/components/chat/ChatInput.tsx

@@ -1652,7 +1652,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
             });
         }
 
-        if (!primaryText && additionalParts.length === 0) return;
+        if (!primaryText && primaryAttachments.length === 0 && additionalParts.length === 0) return;
 
         // Clear queue and input
         if (currentSessionId && hasQueuedMessages) {