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

.env.example

@@ -0,0 +1,6 @@
+# Copy to .env and fill in credentials from your registered Jortt API application:
+# https://app.jortt.nl/new_profile/api/jortt/oauth_applications/list
+JORTT_CLIENT_ID=
+JORTT_CLIENT_SECRET=
+# Optional: space-separated scopes to request (defaults to all registered scopes)
+# JORTT_SCOPES=invoices:read customers:read reports:read