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/graphic-url.ts

@@ -0,0 +1,28 @@
+import { GraphicsPrefix } from "@/src/dict/graphics-dict";
+
+type Params = {
+    graphic_id: number;
+    dark?: boolean;
+    /**
+     * The version shown, so a changed graphic loads afresh.
+     */
+    version?: number;
+};
+
+/**
+ * Where a graphic's sandboxed document is served, in a theme.
+ */
+export default function graphicUrl({ graphic_id, dark, version }: Params) {
+    const query = new URLSearchParams({ theme: dark ? "dark" : "light" });
+
+    if (version) query.set("v", String(version));
+
+    return `${GraphicsPrefix}/${graphic_id}?${query.toString()}`;
+}
+
+/**
+ * The app page that shows a graphic full size, beside the rail.
+ */
+export function graphicPageHref({ graphic_id, bot_id }: { graphic_id: number; bot_id: number }) {
+    return `/admin/bots/${bot_id}/graphics/${graphic_id}`;
+}