feat(composer): send images and text files with steers and follow-ups

[andrebrait]

Summary

omp's steer, follow_up, and prompt with streamingBehavior RPC commands accept images, and omp delivers them with the queued message. omp-web blocked attachments for the whole run and refused to queue a message that had any, so images could only be sent while the agent was idle.

• Attaching through + (file or Paste image), paste, or drag and drop now works while the agent runs.
• Steer and follow-up (Enter, Queue, dictation's send/queue choice, queued web slash commands) carry the attached images. Text files are folded into the message exactly as an idle send does.
• With only attachments in the composer, Stop becomes Queue.
• Edit on an image-only queued message no longer puts omp's [Image] label into the composer.
• Removed the now-dead queueAllowsAttachments predicate and the attachmentsDisabled, dictationKeptWithAttachments, and imagesCannotQueue strings.

The server path needed no change: lib/rpc-manager.ts already validates images on steer and follow_up, and useAgentSession already forwards them.

Known limits

• Images return to the composer from Stop (abort_and_restore_queue) and Edit (remove_queued_message) only with an omp carrying feat(rpc): added abort_and_restore_queue command can1357/oh-my-pi#14179, which adds both. Older omp returns only the text. A queue RPC that fails (steer, follow-up, queued slash prompt) restores its images on any omp.
• Queue actions match messages by text, so two image-only queued messages (both [Image]) are indistinguishable to Delete, Edit, and Steer. This is the existing behavior for identical texts.

Testing

• components/ChatInput.queue-attachments.test.mjs attaches an image and a text file during a run, then checks the steer from Enter, the follow-up from Queue with attachments only, and an expanded /goal queued with attachments. It fails on main because attaching is refused during a run.
• npm test: 1133 passed, 0 failed. tsc --noEmit and npm run lint show no errors.
• RPC smoke against omp 18.6.2 (--mode rpc, gemini-3.5-flash-lite), using the command shapes omp-web sends: two follow_up commands with a red PNG (one with text, one image-only) were sent while the agent was streaming. queue_update listed the text and [Image]; each delivered user message contained image/webp content, and the model answered "Red" both times.

Follow-up commit: images come back

• A failed steer/follow-up/queued prompt, Edit on a queued message, and Stop now return images to the draft (recoverDraft in lib/draft-store.ts carries images). omp's [Image] label is never restored as text.
• Tests: composer test for a refused follow-up; navigation Edit tests now assert the returned images survive draft-key changes and remounts; hook tests assert remove_queued_message images are parsed and Stop restores images from abort_and_restore_queue. npm test: 1134 passed, 0 failed.
• RPC smoke against the #14179 branch (bun packages/coding-agent/src/cli.ts --mode rpc): while streaming, queued two image follow-ups and an image steer; remove_queued_message returned {removed:true, images:[1 image]}, and abort_and_restore_queue returned the steer with its image and the image-only follow-up as [Image] with its image.