Initial implementation: aptly container image, Compose stacks, Helm chart, and Gitea Actions pipelines

Provides a self-contained, containerized aptly (Debian repo manager)
stack with independently releasable image and Helm chart versions.

- images/: aptly-server (aptly built from source, cross-compiled) and
  aptly-deb-builder (nfpm + dpkg-buildpackage) container images
- rootfs/: shared aptly-init/aptly-reconcile/aptly-push/aptly-pack
  scripts consumed identically by Compose and the Helm chart, driven
  by one declarative state.yaml contract
- compose/: test (ephemeral, open) and production docker-compose
  stacks with an nginx read/auth sidecar
- charts/aptly/: aptly-native Helm chart covering every security
  posture from fully open to authenticated read+write, Ingress and
  Gateway API support (usable in parallel for migration scenarios),
  metrics, and declarative repo/mirror/publish reconciliation via a
  Helm hook
- .gitea/workflows/: CI (lint, template, kubeconform, E2E smoke test)
  plus separately tagged image (image/v*) and chart (chart/v*)
  releases, weekly rebuilds, and a preflight workflow validating the
  runner's Docker/Helm-OCI capabilities
- pubkeys/: RSA chart-signing key for Helm --sign / Artifact Hub's
  signKey annotation (Helm can't verify Ed25519 keys)
- docs/, README.md, charts/aptly/README.md: usage, security, and
  versioning documentation

compose/config/nginx.test.conf

@@ -0,0 +1,39 @@
+# Test topology: everything open (security.preset "open" equivalent) — no
+# auth on read OR write. This is what "komplett unabgesichert" looks like.
+# Do not reuse this file for docker-compose.yaml (production).
+#
+# Mounted at /etc/nginx/conf.d/default.conf, which the base image's own
+# nginx.conf already `include`s from inside its own http{} block — so this
+# file must contain ONLY a server{} block (or other http-context directives),
+# never its own http{}/events{}/worker_processes wrapper.
+server {
+  listen 8080;
+  server_name _;
+  client_max_body_size 0;
+  absolute_redirect off;
+
+  location = /healthz { access_log off; return 200 "ok\n"; }
+
+  location = /api/ready   { access_log off; proxy_pass http://aptly:8080; }
+  location = /api/healthy { access_log off; proxy_pass http://aptly:8080; }
+
+  location /api/ {
+    proxy_pass              http://aptly:8080;
+    proxy_http_version      1.1;
+    proxy_set_header        Host $host;
+    proxy_request_buffering off;
+    proxy_read_timeout      3600s;
+    proxy_send_timeout      3600s;
+  }
+
+  location = /signing-key.asc {
+    alias /run/aptly/pub/signing-key.asc;
+    default_type text/plain;
+  }
+
+  location / {
+    root /var/lib/aptly/public;
+    autoindex on;
+    autoindex_exact_size off;
+  }
+}