Add landing page + Caddy download host (site/)

Self-contained, no-JS landing page (tinygrad-minimal) that doubles as the
artifact download host, served by Caddy on an internal :80 box.

- site/index.html: static page, "Same tool, only a little different", feature
  highlights (remote->remote, symmetric panels, ssh_config awareness, edit-in-
  place, self-copy guard, ...), fixed stable download links, FAQ (unsigned notes).
- site/Caddyfile: one flat /dl/ folder with browse + range requests and per-type
  Cache-Control (patches immutable, update.json no-cache, installers short).
- site/deploy.sh: drop a build's artifacts/stable-* into /dl/ (renames the win
  portable zip to a stable name).
- Flat folder matches electrobun's artifacts/ layout, so it's also the future
  updater baseUrl; per-build folders/symlink dropped in favor of it.
- docs/build-and-release.md: document the download host + deploy flow.

Verified: caddy validate + live smoke test (links, cache headers, 206 range,
404 fallback, deploy.sh copy/rename) against a temp root.

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

site/Caddyfile

@@ -0,0 +1,34 @@
+# miniSCP landing page + artifact host.
+# Local / internal, plain HTTP on :80 (no domain, no TLS).
+# Deploy target is /srv/miniscp — see site/README.md.
+
+:80 {
+	root * /srv/miniscp
+	encode zstd gzip
+
+	# Flat artifact feed: these files are BOTH the human downloads AND (later) the
+	# electrobun updater baseUrl. Publishing a build = drop its artifacts/ files here;
+	# stable-named installers overwrite in place, hashed .patch files accumulate.
+	handle /dl/* {
+		# Incremental update patches have unique hashed names → cache forever.
+		@patch path *.patch
+		header @patch Cache-Control "public, max-age=31536000, immutable"
+
+		# The updater feed must always reflect the newest published version.
+		@feed path *update.json
+		header @feed Cache-Control "no-cache"
+
+		# Installers/payloads keep stable names but get overwritten each release.
+		@pkg path *.dmg *.zip *.tar.zst
+		header @pkg Cache-Control "public, max-age=300"
+
+		# browse => directory listing; file_server serves range requests
+		# (resumable large .dmg downloads) by default.
+		file_server browse
+	}
+
+	# Static landing page + assets. No SPA index fallback: unknown paths 404.
+	handle {
+		file_server
+	}
+}