Add Forgejo Actions workflow to build and deploy on push

- .forgejo/workflows/deploy.yaml: build the wasm bundle on the arch-latest
  Docker runner and rsync it into the bind-mounted web root (/deploy) on
  push to master
- deploy/Caddyfile.example: reference site block with the cross-origin
  isolation headers the WASM runtime requires

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

deploy/Caddyfile.example

@@ -0,0 +1,21 @@
+# catcrafts.net Caddy site block
+#
+# The WASM app (Crafter.Graphics) needs a cross-origin-isolated context
+# (SharedArrayBuffer / threads), which requires these response headers. They
+# are NOT optional — without them the page loads but the runtime fails.
+#
+# If you already have a `catcrafts.net { ... }` block, you only need to ADD the
+# three Cross-Origin-* header lines to it. This file is the complete block for
+# reference. Point `root` at the host directory you bind-mount into the runner
+# as /deploy (the "-v /path/to/webroot:/deploy" in the runner's config.yaml).
+
+catcrafts.net {
+	root * /srv/catcrafts.net
+
+	header Cross-Origin-Opener-Policy   "same-origin"
+	header Cross-Origin-Embedder-Policy "require-corp"
+	header Cross-Origin-Resource-Policy "same-origin"
+
+	encode zstd gzip
+	file_server
+}