feat(chat): terminal chat parity for every tool; Desktop-like artifacts

- The chat over a terminal pane now covers Claude, Codex, omp, Cursor and
  Antigravity: Cursor's agent transcript and agy's step log
  (brain/<id>/.system_generated/logs/transcript_full.jsonl) are read as
  conversations; Cursor sessions are claimed by their workspace
- Replies appear as soon as they are written: the projects-tree watcher
  broadcasts `transcript_changed` (at most every 250 ms per session) and the
  chat re-reads the transcript while the terminal underneath draws
- Stop shows from the pane's own busy line (Claude/Codex `esc to interrupt`,
  agy `… esc to cancel`), or fresh output for omp/Cursor — no hooks needed
- Permission prompts read off the terminal become a card with the tool, its
  command and "Deny with a note"; Codex gets Permission mode / Model buttons
  that open its own numbered pickers, answered from the menu card
- Artifacts: cards for pages/documents/diagrams/tables/React components, a
  Preview | Code panel with versions, copy, download, save to the Artifacts
  Hub, full screen; sandboxed iframes without allow-same-origin
- Claude panes get CLAUDE_CODE_ENABLE_TODO_TOOLS=1 so the Progress panel has a
  plan; multi-question pane menus read their Next row and question tabs
- The realtime chat bridge (structured stdio, /api/chat-bridge, /ws-chat)
  from the unreleased ad9d475 is not kept

client/src/components/Sagi/PetChat.tsx

@@ -34,6 +34,7 @@ import {
   chooseRunOption,
   interruptRun,
   readRunMenu,
+  stepRunMenu,
   submitToRun,
   type PaneMenu,
 } from "../../lib/panePaste";
@@ -505,6 +506,9 @@ export function PetChat({
                 if (answerRunMenu(chat.runId, menu, text)) setMenu(null);
                 else setError(t("sagi.chat.notSent"));
               }}
+              onStep={(dir) => {
+                if (!stepRunMenu(chat.runId, dir)) setError(t("sagi.chat.notSent"));
+              }}
               onCancel={() => {
                 if (interruptRun(chat.runId)) setMenu(null);
                 else setError(t("sagi.chat.notSent"));