feat: remove Reflex, archive old app, update docs for Dash migration (Task 5.4)

- Remove reflex dependency from pyproject.toml
- Move pathways_app/ and rxconfig.py to archive/
- Update CLAUDE.md: Dash app structure, callback chain, run command
- All completion criteria validated (10/10 pass)

archive/pathways_app/components/__init__.py

@@ -0,0 +1,17 @@
+"""
+UI components for the Patient Pathway Analysis Reflex application.
+
+This module exports reusable layout and navigation components.
+"""
+
+from .layout import sidebar, navbar, content_area, main_layout
+from .navigation import nav_item, nav_section
+
+__all__ = [
+    "sidebar",
+    "navbar",
+    "content_area",
+    "main_layout",
+    "nav_item",
+    "nav_section",
+]