Add MCP servers and custom tools for bots

Two new settings pages, MCPs and Tools. Super admins define them; super
admins and admins attach them to bots, to workspaces (every bot there),
or to every bot. Bots get them in chat replies and tasks.

- Custom tools: a JSON-schema of arguments plus an HTTP request, a script
  on the bot's computer, or a prompt, templated with {{args.x}} and
  {{env.KEY}}, secrets redacted from results.
- MCP servers: remote (URL and headers) or stdio commands run on the host
  with a setup command and an isolated env, in a per-process pool. Tools
  are listed into a cache and connect on first call.
- Add, edit, access and try open in modals.
- Markdown, JSON and command fields use twui's AceEditor (CodeEditor),
  its scripts loaded on demand.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/components/general/icon-tile.tsx

@@ -0,0 +1,17 @@
+import Span from "@moduletrace/twui/layout/Span";
+import type { LucideIcon } from "lucide-react";
+
+type Props = {
+    Icon: LucideIcon;
+};
+
+/**
+ * An avatar in lists for what has no picture: its icon on a small tile.
+ */
+export default function IconTile({ Icon }: Props) {
+    return (
+        <Span className="size-8 shrink-0 flex items-center justify-center rounded-default-sm border border-solid border-hairline bg-paper">
+            <Icon size={16} aria-hidden />
+        </Span>
+    );
+}