studio: agent window, a chat with a model that edits the scene

✦ Agent in the Studio's top bar opens a floating chat window. The model
(any OpenAI-compatible endpoint with tool calling; default B4L's inference
server, https://inference.p0.contact/v1) gets the 15 MCP tools plus two page
tools (select_object, set_view) and the Studio's state (selection, level,
rotation) in its system prompt. Answers and reasoning stream in; tool calls
show as rows with arguments and results; object ids link to the object;
Stop ends a turn; Undo takes the agent's edits back. The window moves by
its title bar and resizes at its top-left corner.

- studio/agent.js: shared by both front ends (waits for studio.js's
  isokit:studio event); MCP over /mcp or isokit.mcp in the web Studio
- isokit studio: /api/agent/{config,models,chat} relay the calls on their
  own threads (ureq, chunked and flushed per read), so the key stays on the
  machine and the endpoint needs no CORS; settings from ISOKIT_LLM_URL /
  _KEY / _MODEL or agent.json in the user's config folder
- web Studio: calls the endpoint from the page with a key kept in the
  browser; build_web.py --agent-url names a same-site relay as default; the
  deploy builds with /llm/v1, which deploy/Caddyfile forwards to the
  inference server (its nginx refuses the CORS preflight)
- tools/mock_llm.py + tools/agent_checks.py: the agent window checks in both
  check_studio.py and check_web.py

studio/studio.js

@@ -125,7 +125,7 @@
         cancel: function () { if (drag && drag.els) S.view.refresh(); drag = null; }
       }
     });
-    window.__studio = { S: S, view: S.view, op: op, select: select, reloadAll: reloadAll, toast: toast };
+    window.__studio = { S: S, view: S.view, op: op, select: select, reloadAll: reloadAll, toast: toast, api: api, obj: obj, snapStep: snapStep, ready: true };
   }
   function toViewerMeta(m) { return { title: m.title, note: m.note, levels: m.levels, defaultLevel: m.default_level, defaultRotation: m.default_rotation }; }
   function remount() {
@@ -291,7 +291,7 @@
       (S.warnings.length ? "<h2>Warnings</h2>" + S.warnings.map(function (w) { return '<div class="st-warn">' + esc(w) + "</div>"; }).join("") : "") +
       (B && B.agentBox ? B.agentBox(m) :
       '<div class="st-box"><h2>Connect an AI agent (MCP)</h2>' +
-      '<p class="st-help">Agents edit this scene with the same operations as the Studio; their changes appear here live.</p>' +
+      '<p class="st-help">Agents edit this scene with the same operations as the Studio; their changes appear here live. ✦&nbsp;Agent (top bar) chats with one right here.</p>' +
       "HTTP (while the Studio runs):<code>" + esc(base) + "/mcp</code>" +
       "stdio (any time):<code>isokit mcp " + esc(m.dir || ".") + "</code></div>") +
       '<p class="st-help">Select an object to edit it, or pick one on the left to add it.</p>';
@@ -380,5 +380,6 @@
     showVersion();
     renderPalette(); renderLists(); mountView(); renderRight();
     poll();
+    window.dispatchEvent(new Event("isokit:studio")); // agent.js waits for this
   });
 })();