Add a placeholder Evaluations nav entry so the design doesn't get forgotten

Under Settings, next to Referee levels/Forms -- but deliberately not behind
a waffle Flag like the shop/forms stubs, since a flag-gated link disappears
from the nav entirely until someone remembers to turn it on, which defeats
the point of a standing reminder. Visible to MEMBER_ADMIN/ADMIN
unconditionally, links to a bare "coming soon" page (reuses
_generic_list.html with an empty object_list -- there's no model yet).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

management/context_processors.py

@@ -126,6 +126,7 @@ _NAV_SECTIONS = {
     "invoice_list": "invoice_list",
     "form_list": "form_list",
     "submission_list": "form_list",
+    "evaluations": "evaluations",
     "club_settings": "club_settings",
     "onboarding_requirement_list": "onboarding_requirement_list",
     "onboarding_requirement_create": "onboarding_requirement_list",
@@ -171,6 +172,7 @@ _TOP_SECTION = {
     "discount_list": "finance",
     "invoice_list": "finance",
     "form_list": "settings",
+    "evaluations": "settings",
     "club_settings": "settings",
     "onboarding_requirement_list": "settings",
     "role_list": "settings",