docs: add architecture documentation and slides

docs/adr/007-compose-overlays.md

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+# ADR 007: Split Local And Production Compose Overlays
+
+## Status
+
+Accepted.
+
+## Context
+
+Local development needs direct access to service ports, while production must expose only Caddy.
+
+## Decision
+
+Keep `docker-compose.yml` private by default, add `docker-compose.local.yml` for local ports, and add `docker-compose.prod.yml` for Caddy and production environment rules.
+
+## Consequences
+
+The same services run locally and on a server, but exposure is controlled by the chosen Compose overlay.
+