Let users copy the current chat session as markdown

The conversation header menu gets a Copy chat row that puts the active
session on the clipboard as one markdown document: a summary, then each
message under its author and time, with quotes, attachments and
reactions. Bot and workspace refs read as names, message headings drop
below the message headings and code blocks stay untouched. The clipboard
write starts on the click with a pending ClipboardItem so Safari allows
it after the fetch.

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

AGENTS.md

@@ -95,6 +95,7 @@ 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]`. Parsers in `src/utils/*-ref.ts`.
+- **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.
 - **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`.
 - **Attachments:** uploaded on pick (`upload-attachment.ts`, private `media`, text extracted when possible), linked via `bot_message_media`. Replies read files of the last `BotReplyAttachmentMessages` messages. Tasks don't get files yet.
 - **Thinking row / stop:** `bot-busy-state.ts` decides the row's line and whether Stop shows. Stop (`api/admin/bots/stop.ts`, `stop-bot-jobs`) fails every open job of that bot for the user, aborts the running handler (`job-abort-registry`) and drops late face updates.