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/dict/graphics-dict.ts

@@ -0,0 +1,35 @@
+/**
+ * Where the app serves a bot graphic (`bot_graphics`): `/graphics/<id>`,
+ * sandboxed with no network and an origin of its own
+ * (`handleGraphicsRequest`).
+ */
+export const GraphicsPrefix = "/graphics";
+
+/**
+ * Where the libraries a graphic may load are served: `/graphics-lib/<file>`.
+ * A graphic reaches nothing else, so these ship with the app.
+ */
+export const GraphicsLibPrefix = "/graphics-lib";
+
+/**
+ * The libraries a graphic may load, by the file name it loads them under,
+ * read from the app's own `node_modules`.
+ */
+export const GraphicsLibs = [
+    {
+        file: "chart.js",
+        source: "node_modules/chart.js/dist/chart.umd.min.js",
+        description: `Chart.js 4 (global \`Chart\`): bar, line, pie, doughnut, radar, scatter and bubble charts on a <canvas>`,
+    },
+    {
+        file: "mermaid.js",
+        source: "node_modules/mermaid/dist/mermaid.min.js",
+        description: `Mermaid (global \`mermaid\`): flowcharts, sequence, class, state, ER, gantt, pie, mindmap and timeline diagrams from text in <pre class="mermaid">; call \`mermaid.initialize({ startOnLoad: true, theme: document.documentElement.classList.contains("dark") ? "dark" : "default" })\``,
+    },
+] as const;
+
+/**
+ * The message a graphic's frame posts to the page with its height, so the
+ * thread sizes it to fit.
+ */
+export const GraphicSizeMessageType = "cobble:graphic-size";