Migrate to mcdsl: auth, config, csrf, web

- Replace internal/auth with mcdsl/auth
- Replace internal/config with mcdsl/config (embed config.Base)
- Replace internal/webserver/csrf.go with mcdsl/csrf
- Use mcdsl/web for session cookies and template rendering
- Use mcdsl/httpserver for server setup and StatusWriter
- Remove direct mcias client library dependency
- Update .golangci.yaml to v2 format (formatters section)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -0,0 +1,39 @@
+# mcat
+
+mcat is a lightweight web application for testing and auditing MCIAS login
+policies. It presents a login form that forwards credentials, along with a
+configurable `service_name` and `tags`, to an MCIAS instance. This lets
+operators verify that login policy rules behave as expected for a given
+service context.
+
+It follows the standard Metacircular Dynamics engineering standards.
+
+## Quick Start
+
+```bash
+# Build
+make mcat
+
+# Configure (copy and edit the example config)
+mkdir -p srv/certs
+cp deploy/examples/mcat.toml.example srv/mcat.toml
+# Edit srv/mcat.toml with your MCIAS URL, TLS certs, service_name, and tags
+
+# Run
+./mcat server --config srv/mcat.toml
+```
+
+Then open `https://localhost:8443` in a browser.
+
+## Build
+
+```bash
+make all    # vet, lint, test, build
+make test   # tests only
+make lint   # golangci-lint
+```
+
+## Documentation
+
+- [ARCHITECTURE.md](ARCHITECTURE.md) — system design, routes, config reference
+- [RUNBOOK.md](RUNBOOK.md) — operational procedures