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

.gitignore

@@ -0,0 +1,8 @@
+node_modules/
+dist/
+*.log
+.env
+.DS_Store
+
+# Fetched at build time by scripts/fetch-spec.mjs
+src/openapi.json