Add Jortt API MCP server

Model Context Protocol server that exposes the full Jortt accounting API
as MCP tools, generated from Jortt's OpenAPI specification.

- OAuth 2.0 client-credentials auth with token caching and 401 refresh
- 82 tools covering customers, invoices, estimates, expenses, projects,
  bank accounts, reports, labels, ledger accounts and payroll
- Spec fetched at build time (with a runtime fetch fallback), so new API
  operations become new tools automatically with no code changes
- Path/query/body parameters handled automatically; request bodies passed
  under a single `body` argument with a resolved JSON Schema
- Readable, stable snake_case tool names derived from method, path and
  operation summary

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016QhaFvGz9gfRg5qDV3ragu

scripts/fetch-spec.mjs

@@ -0,0 +1,31 @@
+#!/usr/bin/env node
+// Downloads the Jortt OpenAPI specification into src/openapi.json so it can be
+// bundled with the build. Run automatically by `npm run build`.
+import { writeFile, mkdir } from "node:fs/promises";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const SPEC_URL = process.env.JORTT_OPENAPI_URL || "https://api.jortt.nl/swagger_doc";
+const target = join(__dirname, "..", "src", "openapi.json");
+
+async function main() {
+  process.stderr.write(`Fetching Jortt OpenAPI spec from ${SPEC_URL} ...\n`);
+  const res = await fetch(SPEC_URL, { headers: { Accept: "application/json" } });
+  if (!res.ok) {
+    throw new Error(`HTTP ${res.status} ${res.statusText}`);
+  }
+  const spec = await res.json();
+  if (!spec.paths || typeof spec.paths !== "object") {
+    throw new Error("Downloaded file does not look like an OpenAPI spec (no paths).");
+  }
+  await mkdir(dirname(target), { recursive: true });
+  await writeFile(target, JSON.stringify(spec));
+  const count = Object.keys(spec.paths).length;
+  process.stderr.write(`Wrote ${target} (${count} paths).\n`);
+}
+
+main().catch((err) => {
+  process.stderr.write(`Failed to fetch spec: ${err.message}\n`);
+  process.exit(1);
+});