feat(story-mode): save as image, a helper's own steps, a way in on phones, and polish

- Save image: the page as one PNG to share (each panel canvas, then every
  caption, balloon and chip redrawn from its computed style and box).
- The helper drawer lists what the helper did, read live from its own
  transcript (GET .../story/helpers/:agentId), led by the task Claude gave it.
- Session Options has a Story button (same setting), the way in on phones.
- A turn a background task or another session started reads as a notice,
  not as your speech balloon.
- Wide panels keep their scene in a centered stage instead of spreading the
  art to both ends; the fix panel's agent stands next to the page.
- An unchanged page (same ETag) is neither parsed nor redrawn.
- Paths inside the session's folder are shown short; clicks keep full paths.
- Tab stays inside the overlay; a missing 2D context skips the art, not the page.
- A rebindable Story Mode shortcut (no default chord).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.changeset/story-mode.md

@@ -2,4 +2,4 @@
 'aicodeman': minor
 ---
 
-Story Mode draws what Claude Code does as a comic. Turn on **Story Mode** in App Settings → Header buttons (per device, off by default) and its button opens the active Claude session as comic pages: one page per prompt, with panels for reading code, planning, calling in helpers, editing, running tests (POW! or KRAK!), asking you and saving, each with a plain caption anyone can follow. The **Director's cut** switch names every tool call instead and lists all of them beside the page. Everything is clickable: a file opens in the file viewer, the code page shows the exact diff of Claude's edits, a test board shows the output with clickable `file:line` links, and a helper shows what it was asked and what it answered. A turn that is still running redraws as Claude works, new panels inking in where blue-pencil roughs stood. The data comes from `GET /api/sessions/:id/story`, an experimental read-only endpoint.
+Story Mode draws what Claude Code does as a comic. Turn on **Story Mode** in App Settings → Header buttons (per device, off by default) and its button opens the active Claude session as comic pages: one page per prompt, with panels for reading code, planning, calling in helpers, editing, running tests (POW! or KRAK!), asking you and saving, each with a plain caption anyone can follow. The **Director's cut** switch names every tool call instead and lists all of them beside the page. Everything is clickable: a file opens in the file viewer, the code page shows the exact diff of Claude's edits, a test board shows the output with clickable `file:line` links, and a helper shows what it was asked, what it answered and every step it took. A turn that is still running redraws as Claude works, new panels inking in where blue-pencil roughs stood. **Save image** downloads the page as a PNG to share with someone who never opens a terminal. On phones, open it from the session's Session Options. The data comes from `GET /api/sessions/:id/story` and `GET /api/sessions/:id/story/helpers/:agentId`, experimental read-only endpoints.