refactor(routes): move admin_wipe domain into routes/admin_wipe/ subpackage (#5659)

Slice 2h of the route-domain reorganization (#4082/#4071). Moves
admin_wipe_routes.py into routes/admin_wipe/, leaving a backward-compat
sys.modules shim at the old path. Pure file reorganization, no behavior
change.

The shim uses sys.modules replacement so the `import ... as
admin_wipe_routes` + `monkeypatch.setattr(admin_wipe_routes, "SessionLocal",
...)` / `"require_admin"` pattern in test_admin_wipe_gallery.py reaches
the canonical module.

Canonical module imports only from core/, src/, and stdlib (zero internal
routes/ coupling). Zero source-introspection landmines.

Adds tests/test_admin_wipe_routes_shim.py to pin the sys.modules shim
contract. Verified: compileall clean; targeted tests pass.

routes/admin_wipe/__init__.py

@@ -0,0 +1,5 @@
+"""Admin wipe route domain package (slice 2h, #4082/#4071).
+
+Contains admin_wipe_routes.py, migrated from the flat routes/ directory.
+Backward-compat shim at routes/admin_wipe_routes.py re-exports from here.
+"""