chore(v5): archive V5 implementation and remove runtime integration

Move V5 source, migrations, UI, scripts, and tests into documentation, then remove V5 routes, models, jobs, configuration, dependencies, and application hooks.

docs/v5/ui/README.md

@@ -0,0 +1,7 @@
+# Archived V5 UI Prototype
+
+This directory preserves the previous V5 UI source for design and implementation
+reference only. The `.txt` suffixes keep the files outside frontend build and
+source-discovery paths.
+
+Do not import or serve these files. V5 will use a different implementation.