stem95su: host STEM platform for 95. СУ (public NFS-backed static site)

New public static site at stem95su.viktorbarzin.me serving the school's
Bulgarian STEM platform (dashboard + lessons/games, externally authored
HTML/media exported from Gemini).

- Stock nginx:1.28-alpine serving /srv/nfs/stem-site read-only (nfs_volume),
  NOT image-baked — content updated out-of-band (Nextcloud "PVE NFS Pool"
  or rsync), no rebuild; auto-backed-up offsite by nfs-mirror.
- ingress_factory auth="none" (open; CrowdSec + ai-bot-block at the edge),
  dns_type="proxied" (Cloudflare CNAME auto-created).
- nginx ConfigMap sets index stem_board.html (the dashboard) for "/".
- Docs: service-catalog entry + new "Static Site Hosting" pattern
  (NFS-backed vs image-baked) in patterns.md.

Applied via scripts/tg apply; verified live end-to-end (dashboard, 20MB
page, video byte-range, no Authentik redirect) through the public
Cloudflare path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/stem95su/variables.tf

@@ -0,0 +1,9 @@
+variable "tls_secret_name" {
+  type      = string
+  sensitive = true
+}
+
+variable "nfs_server" {
+  type    = string
+  default = "192.168.1.127"
+}