Add Dockerfile for self-hosted deployment, bump build.sh to Zola 0.23.1

Adds a multi-stage Dockerfile (Node for llms.txt generation, the
official Zola image to build, static-web-server to serve) for
deploying via Dokploy/Docker instead of Cloudflare Pages. This is an
additional path, not a replacement - wrangler.toml and the Cloudflare
build.sh remain in place as an option.

Also bumps build.sh's pinned ZOLA_VERSION from 0.22.1 to 0.23.1: the
prior commit migrated every template to Tera v2 syntax (components,
spread operator, native slicing), which 0.22.1 can't parse - confirmed
by a live Cloudflare build failure on this branch. Keeping build.sh
and the Dockerfile on the same Zola version avoids maintaining two
template dialects across the two deploy paths.

Verified: `docker build` succeeds, the container serves the homepage,
a post, the youtube embed, and a proper 404; `build.sh` also runs
clean standalone (simulating the Cloudflare build) and produces a
fully populated public/.

.dockerignore

@@ -0,0 +1,8 @@
+public
+node_modules
+.wrangler
+.git
+manimations/*.*
+/zola
+/zola-v*.tar.gz
+/artifacts