Add bot graphics

Bots can now show a concept as a visual: create_graphic (with
update_graphic, read_graphic and list_graphics, on every run, no computer
needed) stores one HTML document in bot_graphics, per user like the
conversation, and the chat renders its [graphic:ID] ref as an inline card
sized to fit, with a large view and a page of its own (no rail).

Graphic HTML is treated as hostile: it is only served at /graphics/<id>
with a CSP sandbox allowing scripts under an origin of its own and no
network, loading only the vendored Chart.js and Mermaid from
/graphics-lib/. The document carries the app's theme vars and scrollbars,
reports its height to the thread, and a frame that navigates away is
closed.

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

src/utils/link-computer-refs.ts

@@ -1,3 +1,5 @@
+import { GraphicRefHrefPrefix } from "./graphic-ref";
+
 /**
  * The link target a computer ref (`computerRef`) becomes, e.g.
  * `#computer-3`. The chat's markdown renders these links as buttons that
@@ -70,7 +72,8 @@ export const SecretRequestRefHrefPrefix = "#secret-request-";
  * (`[workspace:2]`), file ref (`[file:12]`), folder ref
  * (`[folder:computer:3:seo/raw]`), proposal ref (`[proposal:7]`) and hook
  * proposal ref (`[hook-proposal:4]`), secret ref (`[secret:12]`) and secret
- * request ref (`[secret-request:4]`) in a message into a markdown link, so it
+ * request ref (`[secret-request:4]`) and graphic ref (`[graphic:5]`) in a
+ * message into a markdown link, so it
  * survives markdown rendering as a link the chat can swap for a button,
  * chip or download.
  *
@@ -106,6 +109,7 @@ export default function linkComputerRefs({ text }: { text: string }) {
             /\[secret-request:(\d+)\](?!\()/g,
             (_, id: string) => `[secret request ${id}](${SecretRequestRefHrefPrefix}${id})`,
         )
+        .replace(/\[graphic:(\d+)\](?!\()/g, (_, id: string) => `[graphic ${id}](${GraphicRefHrefPrefix}${id})`)
         .replace(/\[file:(\d+)\](?!\()/g, (_, id: string) => `[file ${id}](${FileRefHrefPrefix}${id})`)
         .replace(/\[folder:([a-z]+):(\d+):([^\]\n]+)\](?!\()/g, (_, volume: string, owner: string, path: string) =>
             `[${path}](${FolderRefHrefPrefix}${encodeURIComponent(`${volume}:${owner}:${path}`)})`,