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/utils/fill-template.ts

@@ -0,0 +1,53 @@
+type Params = {
+    template: string;
+    /**
+     * `{{args.name}}`, dotted paths reach into objects. Missing ones fill
+     * in empty; objects and arrays as JSON.
+     */
+    args?: Record<string, unknown>;
+    /**
+     * `{{env.KEY}}`. A key that isn't set throws, naming it.
+     */
+    envs?: { key: string; value: string }[];
+    /**
+     * Applied to every filled-in argument, e.g. `encodeURIComponent` in a
+     * URL. Envs go in as they are (one may hold a whole base URL).
+     */
+    encode?: (value: string) => string;
+};
+
+const Pattern = /\{\{\s*(args|env)\.([A-Za-z0-9_.-]+)\s*\}\}/g;
+
+/**
+ * Fills a custom tool's or MCP server's template: `{{args.x}}` from the
+ * model's arguments, `{{env.KEY}}` from the envs. Anything else is left as
+ * written.
+ */
+export default function fillTemplate({ template, args = {}, envs = [], encode = (v) => v }: Params) {
+    return template.replace(Pattern, (_match, source: string, path: string) => {
+        if (source == "env") {
+            const env = envs.find((e) => e.key == path);
+
+            if (!env) throw new Error(`The env ${path} isn't set. Add it in Settings, under Environment.`);
+
+            return env.value;
+        }
+
+        return encode(stringify({ value: pick({ value: args, path }) }));
+    });
+}
+
+function pick({ value, path }: { value: unknown; path: string }) {
+    return path.split(".").reduce<unknown>((current, key) => {
+        if (current && typeof current == "object") return (current as Record<string, unknown>)[key];
+        return undefined;
+    }, value);
+}
+
+function stringify({ value }: { value: unknown }) {
+    if (value === undefined || value === null) return "";
+    if (typeof value == "string") return value;
+    if (typeof value == "number" || typeof value == "boolean") return String(value);
+
+    return JSON.stringify(value);
+}