Rebrand sexp → sx across web platform (173 files)

Rename all sexp directories, files, identifiers, and references to sx.
artdag/ excluded (separate media processing DSL).

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

shared/sx/components.py

@@ -0,0 +1,19 @@
+"""
+Shared s-expression component definitions.
+
+Loaded at app startup via ``load_shared_components()``.  Each component
+is defined in an external ``.sx`` file under ``templates/``.
+"""
+
+from __future__ import annotations
+
+import os
+
+from .jinja_bridge import load_sx_dir, watch_sx_dir
+
+
+def load_shared_components() -> None:
+    """Register all shared s-expression components."""
+    templates_dir = os.path.join(os.path.dirname(__file__), "templates")
+    load_sx_dir(templates_dir)
+    watch_sx_dir(templates_dir)