Open bot files in a preview modal instead of a new tab

Markdown rendered, CSV/TSV as a table, images, PDFs, audio, video and
sandboxed HTML in place, other text as code, with Download and Open in a
new tab. Used by file chips, message attachments, the files modal, task
files and the files browser.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

AGENTS.md

@@ -96,6 +96,7 @@ Enables SQLite foreign keys (`enableForeignKeys`), `bunextInit()`, `ensureDocker
 - **Sending:** `api/admin/bots/send-message.ts` -> `enqueueBotReply` -> `wakeBotsQueue`. **Never import `src/bots-queue/index.ts` from a page or API route** (pulls the bunext runtime into page bundles). Optimistic bubble in `pending_messages` until the saved message replaces it.
 - **Composer:** Tiptap editor reading/writing markdown, drafts in `localStorage`, `@` bots / `#` workspaces written as `[bot:ID]`/`[workspace:ID]`. Enter sends (Mod+Enter in lists/code). `@tiptap/react` needs `use-sync-external-store`; the app ships an ESM stand-in in `packages/use-sync-external-store-esm` (file dependency + override; the Dockerfile copies `packages/` before `bun install`).
 - **Rendering:** markdown via `react-markdown` + `remark-gfm`, raw HTML never rendered, component map in `[bot_id]/(data)/message-markdown-components.tsx`. Inline refs, all linked by `link-computer-refs.ts` and rendered by chips in `(partials)/`: `[bot:ID]`, `[workspace:ID]`, `[computer:ID]`, `[file:ID]` (a saved file), `[folder:<volume>:<owner>:<path>]` (opens `/admin/files`), `[take-over:ID:mode]`, `[proposal:ID]`, `[hook-proposal:ID]`, `[secret:ID]` (masked env, Reveal/Copy), `[secret-request:ID]` (masked input card), `[question:ID]` (a bot's questions), `[graphic:ID]` (a bot graphic, framed inline), `[room:ID]` (a chatroom). Parsers in `src/utils/*-ref.ts`. A ref quoted alone in a code span still links; one inside longer code stays literal (`linkComputerRefs` splits out code first). A file chip opens a file from another bot's folder for a user who reaches that folder (`userReachesFileScope`, the same rule as its bytes), so answers passed on from chatrooms keep working.
+- **File preview:** every file link (chips, attachments, files modal, task files, `/admin/files`) is a `FilePreviewLink`: a plain click opens `FilePreviewModal` (markdown rendered with the message elements, CSV/TSV as a table via `parseCsv`, images/PDF/audio/video in place, HTML in a frame with `sandbox=""` (plus the media server's `sandbox` CSP), other text as code, the kind from `filePreviewKind`; Download and Open in a new tab), a modified click still opens a tab. Text is read up to `AppData.FilePreviewMaxTextBytes`. Never render a file's HTML on the app's origin or with scripts.
 - **Copy chat** (header menu): the active session (the one on screen) as one markdown document (`api/admin/bots/conversation-export` -> `conversationMarkdown`, refs as names, message headings demoted). The clipboard write starts on the click with a pending `ClipboardItem` (`copyPendingText`), since Safari drops the gesture after a fetch.
 - **Asking before acting:** `ask_user` (`QuestionsNote`) puts up to `AppData.BotQuestionMaxQuestions` multiple-choice questions (`single` = radios, `multiple` = checkboxes, optional typed "Other") on one card, once per run -> `bot_questions` -> `[question:ID]` chip opening `BotQuestionCard`; the message needs the user. Answers are checked against the questions (`checkBotQuestionAnswers`) and stored, then sent as the user's chat message (`botQuestionAnswersText`); Skip says so. Replies and user-started tasks only: never routines, hook calls or chatroom sessions (no one sees those).
 - **Replies/reactions:** `reply_to_message_id` (not an FK); reactions from the fixed `BotMessageReactions`, toggled by `react-message.ts` and the `react_to_message` tool, pushed as `server:bot-reaction`.