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-ref.test.ts

@@ -0,0 +1,21 @@
+import { describe, expect, test } from "bun:test";
+import graphicRef, { graphicRefId } from "./graphic-ref";
+import linkComputerRefs from "./link-computer-refs";
+
+describe("graphicRef", () => {
+    test("names a graphic", () => {
+        expect(graphicRef({ id: 5 })).toBe("[graphic:5]");
+    });
+
+    test("reads the id back from its link", () => {
+        expect(graphicRefId({ href: "#graphic-5" })).toBe(5);
+        expect(graphicRefId({ href: "#graphic-0" })).toBeNull();
+        expect(graphicRefId({ href: "#graphic-x" })).toBeNull();
+        expect(graphicRefId({ href: "#file-5" })).toBeNull();
+        expect(graphicRefId({ href: null })).toBeNull();
+    });
+
+    test("becomes a link in a message", () => {
+        expect(linkComputerRefs({ text: "Here: [graphic:5]" })).toBe("Here: [graphic 5](#graphic-5)");
+    });
+});