Add sx documentation app (sx.rose-ash.com)

New public-facing service documenting the s-expression rendering engine.
Modelled on four.htmx.org with violet theme, all content rendered via sx.

Sections: docs, reference, protocols, examples (live demos), essays
(including "sx sucks"). No database — purely static documentation.

Port 8012, Redis DB 10. CI and deploy.sh updated with app_dir() mapping
for sx_docs -> sx/ directory. Caddy reverse proxy entry added separately.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/path_setup.py

@@ -0,0 +1,9 @@
+import sys
+import os
+
+_app_dir = os.path.dirname(os.path.abspath(__file__))
+_project_root = os.path.dirname(_app_dir)
+
+for _p in (_project_root, _app_dir):
+    if _p not in sys.path:
+        sys.path.insert(0, _p)