docs: add architecture documentation and slides

docs/adr/006-caddy-production-ingress.md

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+# ADR 006: Use Caddy For Production Ingress
+
+## Status
+
+Accepted.
+
+## Context
+
+Production should expose only the demo UI under `gapido.amiirkhl.ir` with HTTPS.
+
+## Decision
+
+Use Caddy as the reverse proxy and TLS terminator. Route public traffic to `demo-app:8080`.
+
+## Consequences
+
+TLS automation is simple. Internal services remain private on Docker networking.
+